Let's start with a reality check: A much stronger player (MSP) is going to beat you if he plays his level. That's why he's an MSP. But everybody has "off" days, and if you want to maximize your chances of knocking off a MSP (other than simply improving your own game, in which case the opponent no longer is an MSP), then there are three things to focus on:

1. Beat him tactically.
2. Maximizing the chances of the MSP having an "off" day.
3. Maximizing your chances of beating the MSP if he has an "off" day.

How do you beat a MSP tactically? Simple - study his game so you know his strengths and weaknesses, relative to his level. Then develop tactics so that he has to beat you with his "B" game against your "A" game. Does he have a big forehand loop against backspin? Then perhaps serve short, heavy, low backspin to his forehand, and if he pushes it back, either attack or quick push to his backhand, making him attack with his "weaker" backhand. If he attacks the short serve, then you are making him beat you without his big forehand loop against backspin, his biggest strength. But don't forget to bring your own game into account - you want your "A" game against his "B" game.

How do you maximize the chance of the MSP having an "off" day? First, see the first item above - if you beat him tactically, then he's more likely to have an "off" day. It's hard to be at your best if your opponent won't let you use your best shots! But the other major way is to use lots of variation so the MSP never gets into a rhythm. Mix up your serves, your receives, your pushes, your blocks, your loops, and everything else.

How do you maximize your chance of beating an MSP if he has an "off" day? First, focus on the two items above - beating him tactically and varying your shots so the MSP never gets into a rhythm. But then you need to focus on one simple thing: You must play well yourself. That means staying relaxed and just letting yourself go, but without overplaying that just leads to mistakes. Don't think of the MSP as a "Much Stronger Player." He's just a big fish you've hooked, and so all you have to do is focus on reeling him in. I hesitate to say this, but the biggest cause of an MSP coming back and winning is when the MWP ("Much Weaker Player") realizes he's about to beat an MSP, and mentally falls apart. MSPs are generally very strong mentally - that's why they are MSPs - so you have to be just as strong mentally as they are.

Why did I hesitate on saying this? Because the very act of thinking about beating an MSP in a match is the biggest cause of choking it away, and my mentioning it may make you think about it as well. But you need to prepare yourself in advance of the match against the MSP so that when you are in that position to win, you are mentally ready to play it all the way to the end without thinking about actually winning or losing. So just think of him as that fish you are reeling in, and keep reeling!

If you think of yourself as an Olympian when you play, you'll play better than if you think of yourself as some scrub at a club. But how can you psychologically pretend to be an Olympian, and how does that help? Great question - and here's The Twelve Core Psychological Characteristics of Olympians from Psychology Today. I was going to write about each point, but why do that when they've already done it so well in the article?

The key question to ask yourself is this: Do you have a better chance of playing really well if you imagine yourself as a player playing really well? Once you realize that the answer there is a decided YES, go through the twelve items below, one by one, and grade yourself on how you do on each. If you get a good grade on one, good for you! If you get a bad grade on one - you know what you have to do. Here are the twelve:

1. The ability to cope with and control anxiety. 
2. Confidence 
3. Mental toughness
4. Sport intelligence
5. The ability to focus and block out distractions
6. Competitiveness
7. Having a hard-work ethic
8. The ability to set and achieve goals
9. Coachability
10. Hopefulness
11. Optimism
12. Perfectionism

The first four are psychological, the rest are tactical ideas.

1. Remember the mentality and feel of a great match you've played, and get back into that mode.
2. Take ten seconds to stare at something in the distance to clear your mind.
3. With nothing to lose, relax, have fun, and just play.
4. Ignore the score and just play the next point. Repeat.
5. Attack elbow with backhand. Most players have trouble against an aggressive shot right at their playing elbow, and the easiest way to do that is with the backhand, where you are facing the opponent and so can see his elbow. Do it over and over in rallies and watch him crumble. (Exception - if you're playing an all-out forehand attacker, then go for the wide corners.)
6. Short no-spin serve. They are harder to push heavy, low, or short, and tend to pop up. And if the serve is very low, they are surprisingly hard to attack effectively. So serve and attack! Mix them up with backspin serves.
7. Slow, spinny, consistent loops. Missing your loop? Then slow it down and go for lots of topspin. You'll be surprised how many players fall apart against this.
8. Quick-push serves back wide. Can't stop the opponent's serve and attack against your push return? Are you giving him easy pushes, or are you quick-pushing the serve quick off the bounce into a wide corner? To the backhand will likely disarm him, to the forehand will likely catch him off guard. (If you have good touch and have practiced this, you can also push them short.)
9. Stop and think about how you are winning and losing points. Then pick a winning service pattern, and one or two other tactics that will win.
10. Talk to a coach or top player between games or in a time-out. He might see something you have not. Or just talk to anyone between games, and you'll be amazed at how talking it out makes it obvious what you need to do.

One of the things coaches stress is that you should be aggressive against deep serves. (A short serve means that, given a chance, the ball would bounce twice on your side; a long serve would only bounce once.) Against a short serve, you can rush and angle the server by taking the ball quick off the bounce, plus you can drop the ball short. But against a deep serve, you can't do this, so a passive return gives the server an easy attack. If the server has a weak attack, that might be okay, but in most cases, if you don't attack deep serves, you put yourself at a disadvantage as the server gets an easy attack.

But to attack the deep serves you first have to recognize that the serve is long. How do you do this?

Imagine an outfielder in baseball running down a fly ball. (Or any other sport that involves judging the trajectory of a thrown or hit ball.) He doesn't do mathematical calculations to judge where the ball will drop. He simply watches the ball as it rises, and from that, with experience, he learns to judge the arc the ball will take. And so, after time, a good outfielder can immediately run to almost exactly where the ball will drop.

It's the same thing in table tennis - not just in judging whether a serve is long, but on ANY shot. With experience, you learn to judge, as the ball is leaving the opponent's paddle, where it will go. (Advanced players take this to another level and often know where the ball is going before contact, by watching the ball and racket as they approach each other.) When an opponent serves, it's the same thing. Watch his paddle, and as the ball bounces off of it, you should be able, with practice, to almost instantly judge its trajectory. If you can do that, you'll immediately know if it's long or short.

More specifically, you'll see how fast the ball comes off the paddle, how downward it travels (which lets you know high it will bounce, which is part of the trajectory), as well as the spin. (Topspin will make it bounce out at you, and so usually goes long, while backspin slows it down, and is more likely to pull the serve short.) Advanced players can judge the depth reflexively as the ball is leaving the paddle or sooner. With practice, you should be able to do so before the ball bounces on the server's side of the table.

You do have to judge it quickly as it takes time to set up an attack. So how can you practice this? Get a coach or practice partner and have them serve to you! Ideally, have them do "half-long" serves, where the second bounce, given the chance, would either bounce very close to your end-line, or just off it. You get to judge which it is. It can be difficult to tell if a ball is going to go one inch long or short, but you should be able to judge it so that if the ball goes six inches off, you always loop it. And then four inches, and so on. Top players are masters of judging this to within an inch or so, and instantly jumping on serves that go too long.

These are both great incentives in practice. Some want to win so badly that they'll practice, hour after hour, to achieve their goals. Others hate losing so much that they'll use it as incentive to train forever to avoid it. A little of both often helps.

The problem comes when you have to play a match - and that's when hating to lose becomes a problem. For some, it might help in practice, but in a match it's a quick way to choke away as you nervously play to avoid losing rather than playing to win. If you play to win, then you'll focus on doing what's needed to win, and you'll be so focused on that that you won't even think about losing, and so won't get nervous or choke.

Where are you on the "Want to Win" vs. "Hate to Lose" spectrum? Here's a simple test. If, at the instant that you lose a close match, you are surprised, that means you were focused on winning, which is what you want. If, however, you are not surprised at that instant, you were focused on not losing, and that very type of thinking might be what brought on the loss.