One of the best ways to improve is through multiball training, and one of the best drills you can do there (besides an intense stroke workout) are random drills. When you play a match, you don't know where your opponent is going to put the ball, so you have to be ready to cover the whole table.
A beginner or anyone working to develop their strokes should mostly do rote drills, where the player knows where the ball is going each time so they can focus on the stroke itself. At the advanced levels they still do rote drills, but mostly to tune the strokes and develop faster and faster footwork. As players develop, and especially at higher levels, players do more and more random drills. This allows them to develop the nearly instant reactions to incoming shots that they will face in a match.
You could, of course, just play matches, which is the ultimate random drill. But while that's important, you also want to focus on specific shots to react to. For example, if you want to react to whether a fast incoming ball goes to your forehand or backhand, you can get limited practice with this in a game, with perhaps two or three shots per rally, and then go pick up the ball. Or you could have a coach feed continuous multiball, and you get maybe twenty times the practice on this in the same amount of time.
A problem with random drills is that you can't really do them very well live (i.e. with a practice partner) until both players are relatively advanced. And so players generally don't do them until they are somewhat proficient - and then they practically have to start from scratch doing random drills that they should have been doing early on. Once you can hit a decent forehand or backhand you should be doing some sort of random drills as well. Few do so.
So get a coach or a practice partner you can take turns with, and do random multiball drills. At first have them feed the ball randomly to two spots - middle forehand and middle backhand. Make sure your first move is the right one; you have more time than you think, so don't rush. When you are comfortable at doing this at rally speeds, then go random the whole table. Learn to cover all five spots - wide forehand, middle forehand, middle, middle backhand, and wide backhand.
Let me emphasize - the key is that the first move must be the right move. No moving to the forehand and then changing when you see the ball going to the backhand, or vice versa.
Once you can do this proficiently in multiball, you should practice it live. Ideally you would at first do this with a coach or top player, who can control the ball well and keep the rallies going. But in most cases you'll need to do this with a practice partner who is more your own level. For this drill, you would play all of your shots to the same spot, either to your practice partner's backhand or forehand. As with multiball, start by having your partner hit randomly to just two spots (middle forehand or middle backhand), where you have to react properly to both shots and consistently drive the ball back to the pre-arranged spot. When you are proficient in this, then have your partner place the ball all over, in particular to the middle, which is often the hardest spot to cover. (Here's a Tip of the Week, "Covering the Middle.")
When you are proficient at this drill in all its variations, and at speeds that approach match speeds, you will be able to do the same in a match, and your rallying ability and overall level will shoot up.
Here's a short video (26 seconds) of Soo Yeon Lee doing random multiball. She's hitting; depending on your level and playing style, you can do this hitting or looping.