One of the axioms of coaching is that you can't fix technique in the middle of a match. Whether coaching someone in a match, or trying to make adjustments yourself in a match, technique is something that needs to be honed in practice so it becomes automatic (i.e. subconscious) in an actual game. The reason for this is that the game is mostly played subconsciously. You don't consciously do technique very well in a game situation, or even choose the proper racket angle - your subconscious does all this after you've honed it in practice. There are just too many things to remember to do for one to do so consciously; the minute you take conscious control all that training is out the window. To fix something in mid-match means to consciously take control, and that rarely goes well.

This is why the conscious mind's task during a match is mostly tactical - choosing what serves to use, how to receive, how to rally, etc. (And even there, much of it becomes subconscious - for example, when your conscious mind decides to attack deep serves, for this to work the subconscious has to get the message so it does so automatically.) The conscious mind should also focus on sports psychology - but that's basically techniques to get the conscious mind out of the way so the subconscious can take control.

There are a few times when you can make basic fixes to stroking problems, though not necessarily technique problems. (I will write this as if I was coaching a player in a match, but you can do this yourself, i.e. coaching yourself in the same way.)

Suppose your player lifts way too much when looping or smashing, and keeps going off the end. (There could be a dozen technical reasons for this; he might be standing up too straight, or using too much arm, or not transferring his weight forward, etc.) Trying to fix his technique directly probably won't work - that's something you'll have to do after the match, when you can zero in on the specific problem and drill the player to do it properly. So what can you do? Instead of trying to fix the technique, understand that the poor technique is putting the ball off the end when it aims for the table. So change the target; tell the player to aim for the top of the net. If the player makes a conscious decision to aim for this, and then lets the subconscious do this, it'll probably get the message and aim for the top of the net - and will likely do just what it was doing before, i.e. aiming too high, and so it'll instead go over the net and hit the table.

Suppose your player has, say, a wristy forehand that causes him to lose control. Telling him to change his technique isn't going to help in that match; it'll just put him in the position of trying to learn a brand new technique, i.e. a wristless forehand he hasn't used before. His subconscious doesn't know what to do, and so you essentially turn the player into a beginner, at least with this one aspect. You could, of course, think of the match as just practice and have the player focus on the technique. Then it's not really a "match" so much as a practice session. But it's a highly inefficient practice session as the player will only haphazardly get to use the shot in question, and when it comes up, guess what? He'll reflexively do what his subconscious is used to doing, i.e. the poor technique. That's why to fix technique you have to practice it in a drill situation, where you do it over and Over and OVER until it is so honed that the subconscious can do it in a match. If it can't, then it'll fall back on old habits during the match, and re-enforce the bad habit.

Suppose your player is standing up too straight, which leads to all sorts of technique problems, such as lifting too much when looping. If he's used to standing up straight all the time, there's not a lot you can do in the middle of a match. On the other hand, if the player sometimes stays low but other times (perhaps in the pressure of a match) stands up too straight, reminding him to stay low is a simple message that the subconscious can get since it's used to staying low, and it solves the technique problems.

Sometimes it's not a technique problem so much as adjusting to something the subconscious hasn't seen before, and so isn't able to react properly. For example, suppose my player keeps blocking an opponent's slow, spinny loops off the end. The player hasn't seen such spinny loops before (at least not enough for the subconscious to learn what to do automatically), and so nearly every block goes off. I could tell him to close his racket angle - but that probably wouldn't work. In a game situation the subconscious automatically chooses the racket angle, and trying to adjust this against these super-spinny loops in the middle of a match is slow and difficult. If you tell your player to close the racket more, and he tries to do so consciously, he will likely lose what little control he had as his conscious mind can't reflexively do the proper angle in the split second it has to do so, and will tend to fall back on the reflexive angle that wasn't working before. So consciously telling oneself to close the racket more isn't really that helpful - the subconscious can see that it's blocking off the end, and is already trying to make adjustments (often too slowly) if you let it. (The more you play the easier these adjustments become.)

However, if you tell the player to block more aggressively, then the spin won't take on the paddle as much, and the player won't be as susceptible to heavy topspin as before. It's a simple message to the subconscious - "block harder!" - and as long as it's not overdone ("harder" doesn't mean "smash"), it will often solve the problem.

Here's my recommendation: focus on developing proper technique in practice, not in matches. Work with a coach or top player if possible, or watch videos. Get the technique down before using it in serious matches. It's okay if you don't yet have the timing for the techniques as long as you are doing it mostly properly. Matches are a great way to learn, but they are not the place to develop technique. 

Everyone has a weakness in their game or a shot they'd like to perfect. How do players go about addressing these problems? Usually in haphazard fashion. They'll either try to work on it in actual matches, or they'll work on it some in practice, along with everything else. The result is usually a little improvement, which often convinces them they are on the right track. And so they progress very slowly. But it can be done much quicker with a little "saturation training."

What this means is that for a time you should focus almost entirely on whatever it is you are trying to improve. It means devoting both practice time and match play to the single-minded goal of improving a weakness or perfecting a strength. You can still practice other things, but during the time of saturation training this should be kept to a minimum, and mostly to maintain other aspects of your game. The saturation training should include lots of shadow practicing the new technique as you work to ingrain it. 

Let's say you want to develop a backhand loop against backspin. You could practice it for 5-10 minutes with a partner, and then look for chances to use it in a game against your usual practice partners. Or you could arrange to practice it for perhaps an hour a day for a time, and arrange practice matches specifically around developing this shot. Let's look at both of these methods of practice, using the backhand loop against backspin as an example.

How do you practice the backhand loop against backspin? Ideally, find a coach or player who can feed multiball to you and go at it. (Make sure to have a coach or top player help you out first so you do it right.) Or practice it against a robot, though don't do this exclusively - you want to learn to react to a ball coming off a racket as well. Or have someone just push your backspin serve back over and over so you can practice the shot. (But remember that you get many more shots per time with multiball or a robot.) Do the shot over and Over and OVER until it is so ingrained you can do it in your sleep. It has to become muscle memory, and that doesn't happen by practicing it haphazardly now and then. You have to practice it relentlessly until it becomes a part of you.

Once the shot is pretty much ingrained in this way, you need to use it in practice matches. And here is where many players make a major mistake - they look to use it against their peers, who may not give you the shot you want. Instead, seek out someone who will normally push your serve back right at your backhand, allowing you to use the shot over and over. Or someone who will serve and push, allowing you to backhand loop. This usually means playing a weaker player, where you can control the start of the rally and get the shot you want to practice. Get the shot ingrained in this way as something you can do regularly in a match.

It's only after this that you would focus on using it in matches against your peers. Now you might not get as many easy chances to do the shot, but when the chance comes, hopefully it's now so ingrained you'll do it automatically. And at this point, it is part of your regular repertoire.

Whatever shot you are trying to perfect, use the same type of thinking shown here to saturate your practice so you can develop the shot. And then keep developing it, while perhaps sometimes using a little saturation training to develop other parts of your game. 

"Real Tactics" are the tactics that a player should use in a given match to maximize his chances of winning. "Parroting Tactics" are the tactics that many players use because it's what everyone seems to be doing, and so they figure (consciously or subconsciously) it's what they should be doing as well. When two players of equal ability play, and one uses "Real Tactics" and the other uses "Parroting Tactics," guess who usually wins?

The classic example of "Parroting Tactics" would be rarely serving deep to the forehand. At the higher levels, if you serve deep to the forehand, the opponent almost always loops, and the server is at a disadvantage. And so at higher levels you rarely see deep serves to the forehand except as an occasional surprise. At lower levels, opponents often cannot loop effectively or consistently against deep serves to the forehand, and usually have better control on the backhand side, and so are much better if the opponent serves to their backhand side - which most players obligingly do, since that's what they see stronger players doing.

There is some argument to the idea that a player should play higher-level tactics if he wants to be a higher-level player, and so should avoid serving deep to the forehand since that's generally not a higher-level tactic. But this misses the point. The higher-level tactics that usually goes on in higher-level matches is not about avoiding serving deep to the forehand because others don't do that; it's about zeroing in on the opponent's weaknesses and going after them. They don't think, "I'm a higher-level player, and so I shouldn't serve deep to the forehand." They think, "My opponent has a strong forehand loop, and so I shouldn't serve deep to the forehand." The same higher-level tactics, if applied at lower levels, would be, "My opponent has a weak forehand loop, and so I should serve deep to the forehand." And that's what most lower-level players should do, if the tactic works.

You don't develop higher-level tactical skills by playing weak tactics. You develop them by playing strong tactics, i.e. "Real Tactics." If the opponent has a weak forehand loop, you serve to it, no matter what the level. Against six-time U.S. Men's Singles Champion David Zhuang, a pips-out penholder, most players would serve short (which he was very good against) or long to his backhand (allowing him to control the backhand diagonal, which he was also very good at doing), rather than serve long to his forehand, where his pips limited the effectiveness of his receive and where he'd be drawn out of his favored backhand position. A few players figured this out and would regularly serve long backspin to his wide forehand (often "half-long," so the ball barely went off the end), and then counter-attack effectively to his open backhand side.

I once coached a player who had lost the first game at deuce after serving over and over to his opponent's strong backhand. I told him he should both serve AND receive every ball to the opponent's weak forehand until the opponent won two points in a row. I even had him serve from the middle and forehand side so he could get a bigger angle into the forehand side. My player went up 9-0 before losing a point, and won the next three games easily by relentlessly going to the opponent's forehand side.

Obviously there is a limit. If the opponent knows you are going to the forehand, and you do so over and Over and OVER, he might get used to it. So you would mix in shots the other way, especially if the opponent is camping out over there. But guess what? If your opponent does camp out on the forehand side to protect that side, then his backhand opens up, and so you go there. That's "Real Tactics." "Parroting Tactics" would be to continue to go to the forehand because the player read an article that says he should go over and over to the opponent's weak forehand. 

Many players understand the need to serve short (in addition to long serves), since short serves stop the opponent from looping. More advanced players learn the control to serve "half-long," so the second bounce, given the chance, would be right about the end-line. However, many players who serve short do not think about the placement. There are five: short to the extreme forehand, middle forehand, middle, middle backhand, and extreme backhand. Here are the advantages and disadvantages of each. (Some of these are written as if both players were righties. It would be a long article if I covered all possibilities.)  

Every opponent is different, so test each of them out on these five types of placements and see which one works best for you.

Extreme Forehand

• Advantages: It makes the receiver reach way over the table, often leading to awkward returns. To guard against this the receiver often has to stay close to the table, making him vulnerable to deep serves, especially to the wide backhand. After returning these serves the receiver may have trouble getting back into position.
• Disadvantages: It gives the receiver a big angle crosscourt, and also gives maximum table as a target, since there is more court diagonally than down the line. To guard against this angle, the server might not be able to effectively cover down-the-line receives. For a righty serving to a righty, this means the receiver can flip to the wide forehand, and to cover this, the server may have to move to his right, leaving the backhand side vulnerable.

Middle Forehand

• Advantages: It takes away some of the angle into the forehand and gives less table to flip into. It also forces the receiver to move in differently than against the wide angle - often having to step slightly to the left (for righty versus righty) - and some players have trouble doing this.
• Disadvantages: The receiver doesn't have to move as far in, so can get in and out more quickly. The receiver also now has a slight angle into the backhand as well as into the forehand. It also allows a receiver with a strong backhand flip (especially a "banana flip," a heavy topspin/sidespin attack against a short ball with the backhand) to more easily step over and use the backhand.

Middle

• Advantages: Receiver has to decide in a split second whether to receive forehand or backhand. Serving to the middle takes away the extreme angles in both directions, and leads to the least amount of table the server has to cover. It gives the receiver the least amount of table to receive to since there are no long diagonals from the middle. This is the most popular location for elite players, though of course they vary it.
• Disadvantages: Receiver can more easily use their stronger side for receiving, forehand or backhand. The receiver can angle the ball equally to both sides.

Middle Backhand

• Advantages: Only gives a slight angle into the forehand side, so the server can often follow the serve with a forehand from the backhand side. If the serve goes slightly long, he might still get a backhand return instead of a forehand loop.
• Disadvantages: It allows the receiver to receive backhand without having to reach too much over the table. It gives an angle into the backhand and some angle to the forehand. It's the most common serve at the beginning and intermediate level, so those players are used to this.

Extreme Backhand

• Advantages: It takes away any angle into the wide forehand (for righty versus righty), and so the server can try to cover the backhand side with his forehand, knowing that if the receiver does give an extreme angled return, he can always switch to backhand. It brings the receiver well over the table, making him vulnerable to deep ball on the next shot. If the serve goes slightly long, you'll most likely get a backhand return instead of a forehand loop.
• Disadvantages: It gives the receiver an extreme crosscourt angle. It takes away any indecision from the receiver since he'll almost always receive backhand.

Want to learn a really spinny pendulum serve? Not just a get-the-ball-in-play one that anyone can return, but one with great spin? One with so much spin that the backspin serves will come back into the net and sidespin ones will break sideways as if yanked by a string? Here's how. (The instructions assume you are right-handed; lefties adjust - sorry.)

Step One: Go to YouTube and put "pendulum serve" in the search box. Lots of videos will come up - study them! Study them. You want to have a good idea of what you are aiming to do.

Step Two: Hold the racket out in front of you, forehand side pointing up. (You don't need a table for this.) Toss a ball up, and on the drop spin the bottom of the ball with a right-to-left motion. The ball will jump some to your left. Now tilt your racket slightly so the left side rises (i.e. clockwise). Now repeat, this time contacting the ball on the bottom-left. Now you should be able to spin the ball so that it goes straight up. Catch it and do it again. Do this over and over until you can really spin the ball, and so that it goes straight up. This is how you learn both to spin the ball and to control it. Make sure to just graze the ball - the goal is to make the ball spin. If you do this exercise regularly, pretty soon you be putting tremendous amounts of spin on the ball.

Step Three: Repeat step two, except now go back to spinning the very bottom of the ball. The ball will jump to your left some; catch it. Again, the goal here is to both spin the ball and control it. You need to be able to control how far the ball jumps to your left before you go to the next step.

Step Four: Now you are ready to try this on a table. Repeat step three, except don't catch the ball - let it go. You should now be able to spin the ball and control it, and so should be able to control where it bounces on the table. Practice this until you can spin the ball and control it so it bounces over the net after one bounce, a legal backspin serve. Remember that the contact point is nearly the very bottom of the ball. Don't worry about the height of the serve; focus on great spin and control. When you get good at this, the ball will come to a stop on the far side, and even bounce backwards. Top players can put so much backspin on the ball that it practically jumps back into the net.  

Step Five: Now focus on contacting the ball very low to the table, perhaps six inches high, and keeping the ball low to the net. The lower your contact point, and the finer your grazing (i.e. more spin, less speed), the lower it will tend to bounce.

Step Six: Go back to YouTube and again put "pendulum serve" in the search box. Study them! The above is a great way to learn to put backspin on the ball and control it. Now learn to contact the ball with a sideways motion for sidespin-backspin and sidespin. As you get better at it, you'll learn to contact it on the upswing of the pendulum swing for sidespin-topspin. Once you can serve with heavy backspin and control it, it's not that hard to learn the same with other spins.

Step Seven: Now it's time to learn the Reverse Pendulum Serve. As above, start by going to YouTube and put "reverse pendulum serve" in the search box. Repeat the steps above, except now the racket tip points toward you - but otherwise it's exactly the same each step of the way. Good luck!

A few key points to remember:

1. Serving is a violent motion. If you want the ball to have lots of spin, you need your racket to move at high speed. That means using your service motion to drive the wrist into the serve, with the wrist snapping into the ball just before contact.
2. Graze the ball near the bottom. (Contact more toward the back of the ball only if you are serving longer and faster.) However, until you learn to really graze the ball very finely you'll end up serving high when you do this. To compensate, contact the ball slightly toward the back of the ball.
3. To keep the ball short, the first bounce on your side of the table should be near the net. However, if you want the ball to go half-long, so second bounce is near the opponent's end-line, the first bounce should be more in the middle of your side of the table (depth-wise).