Nearly all top athletes are creatures of ritual. This isn’t superstition; it’s a way for them to systematically be at their best. This includes finding little ways to always be at their best physically, mentally, tactically, and equipmentally. (Yes, I just coined that term.)

• Physically, this means preparing for play the same way each time. This includes getting enough sleep at regular hours; eating properly (and a lot if you train a lot); hydration; and proper warm-up. Warming up isn’t just at the table; it means doing, for example, some easy jogging and stretching before play to get the body ready. Once at the table, it means going through a systematic practice routine that allows you to warm up and tune up all of your major techniques. It also means having snacks and drinks ready during a session.
• Mentally, this means preparing yourself so your mind is at its best for play. This is probably the most overlooked area. Nearly all top athletes have a routine for this. For example, many listen to music, often a specific song or musician, which gets them mentally ready. Others meditate to clear their minds. Most top players develop little rituals at the table as well, perhaps tapping the table with their hands or bouncing the ball a certain number of times before serving. Everyone needs to find their own way of doing this.
• Tactically, this means going over the tactics of the upcoming match (assuming you are about to play games). If you know the opponent (either from playing, watching, or scouting him), then you should decide what the most important things to remember should be, and usually get it down to a few simple items, such as 2-3 serves, 1-2 receives, and 1-2 rallying tactics. (This is slightly more than what a coach should tell you, but you should be able to deal with a few more things on your own, since you are choosing them.) Above all, remind yourself to stop and think about these things periodically during the match to make sure you are actually executing the needed tactics. The tactics should be flexible, and change as needed, but you should make a habit of always having a rough plan. If you don’t know the opponent, then your tactics should focus on what you want to do, and adjust as you learn how your opponent plays – which shouldn’t take long.
• Equipmentally, this means having the proper equipment on hand. There’s the obvious: your racket, covering, and shoes. Make sure they are in good condition. Then there’s the less obvious: backup rackets, towels (especially if it’s humid), and a wet cloth or paper towel to step on between points if the floors are slippery. Make a habit of making sure you have everything present and ready. 

Playing backhands at the start of a rally is easy, since you are in position. But what do you do when you've been moved to your wide forehand, and have to move quickly to cover the wide backhand? You have three movement options - diagonally in, diagonally sideways, and diagonally back.

1. Diagonally In. For this, you would move in to cut the ball off quickly, before it has a chance to get past you. If you are a close to the table player, then this is what you'd want to do. You also might want to do this if you were moved off the table when covering the forehand; moving in gets you back to the table. By moving in and taking the ball more quickly, you rush the opponent, or at least don't give him time to wind up for his next shot. When moving in like this, most players block or drive the ball. At the advanced levels players can move in and backhand loop the ball, often on the rise. The downside of moving in, of course, is that you have little time, and so either simply don't have time to do so, or are rushed and so make mistakes. You don't want to rush your shots, so only move in if you have time, or if you are doing a relatively simple block.
2. Diagonally Sideways. This is the most common way, and what I'd recommend for most players. This gives you time to do your best backhand shot, whether driving or looping, without backing up so much that your opponent has too much time. If you want to improve, you should endlessly practice moving side-to-side where you move mostly sideways. Many players may have a small diagonally in movement when covering the backhand because most players tend to take the ball quicker on the backhand side than the forehand, but if it's only a little, then it's essentially sideways.
3. Diagonally Back. This is a defensive method, and should normally be done only when absolutely forced to. Players who strongly favor the forehand often find themselves rushing about playing the forehand, and when moved to the wide forehand, often have to back up to cover the wide backhand. If you are forced back in this way, you will most likely be spinning soft with the backhand or fishing, or (if really in trouble) chopping or lobbing. (If your style of play is chopping, then there's nothing wrong with this. But if you are an attacker who is forced to chop because of this, then you are probably at a disadvantage if forced to chop.) If you find yourself forced back in this way on the wide backhand, there are two things to consider. First, try and make your shot as effective as possible, given the circumstances - and that mostly means keeping your ball deep, ideally with good topspin. Second, consider what got you into this situation in the first place, and find ways to avoid this situation. 

Think about the last time you played a match and got nervous. Now ask yourself this: What were your tactics in that match? If you are like the overwhelming majority of players I've worked with over the years in that situation, you probably didn't have a strong game plan - you were probably just winging it. And so, unsure of what you were doing, you were (drum roll please) . . . unsure of what you were doing. And it is that lack of surety that often leads to nervousness.

So next time you are nervous, ask yourself what your game plan is, and come up with a coherent one. Not only will this give your mind something to think about other than worrying about your upcoming doom, but it will give you the confidence that you know what you are doing. You still have to execute the shots, but it's a lot easier to be confident when you know what you are doing than when you don't. Plus, this confidence allows you to think a bit more clearly and so play even better tactics. In other words:

Good Tactics => Confidence => Good Tactics => Even More Confidence

Let's break this down. Suppose you get nervous in a match. Rather than just tell yourself not to be nervous, think tactically. Ask yourself what tactics you need to do to win. Keep it simple – that is key. Then execute those tactics in a flexible way. (Flexible as in be ready for anything, but use tactics to increase the chances of the rallies going the way you want them.) If you focus on simple tactics and execution, you may find the nervousness melting away as you've given your mind something simple to focus on. This leads to confidence and a clear mind, which leads to clear thinking and continued good tactical play, which leads to even more confidence. It's an upward spiral that leads to playing your best – or, as it's often called, playing in the zone.

When I talk to players after losses, often they'll blame their loss on nervousness. It's only when I question them that the whole truth comes out! 

Many players play table tennis like they were playing pinball. They stand there, and when they have to move, they mostly just reach for the ball. The reason for this is a combination of two factors: they are not ready to move, and they are not in the habit of moving. These are two separate things. 

A coach could stress the proper ready stance and the importance of moving, and try to get the player to be ready to move and to develop the habit of doing so. And it might sink in. But there's an easier way. Put your racket aside. Now imagine you are covering someone in basketball. (Or an infielder in baseball or a goalie in soccer.) Don't think about it; just do it. Then examine what happens. Almost for certain your feet went a little wider, your weight went on the balls of the feet, your knees bent some and pointed outwards slightly, and you leaned forward slightly at the waist. Your knees were suddenly bouncy as you prepared to move in either direction. (You probably raised your arms as well; you can drop them now, but keep the free hand up some for balance.) You are now in a perfect ready position! 

You are now ready to move. Do this regularly, and you'll develop the habit of moving. Your pinball days are over. 

When you serve, whether in a match or when practicing, you should always first visualize the serve in your mind. You should see the serve's entire path and everything it does before serving - the contact off your racket, its speed and spin, the first bounce, its path over the net (low, any curving due to spin), the second bounce on the far side, and where it bounces after that. You should also feel the contact in your head, whether a grazing contact to create great spin or sinking more into the sponge for more speed.

Then serve, and observe if the reality matches what was in your mind. This gives feedback so that you can learn to control and develop the serve. Most players who have trouble controlling their serve (i.e. most) do not use this feedback, and so it's no surprise they can't control their serve. This also allows you to improve the serve by visualizing as it should be, and striving to match that.

When practicing, perhaps play a game with yourself where you visualize different serves, and see if you can match what's in your head. Practice until you can do this with all of your serves, including both spin serves and fast, deep serves. Perhaps even put targets on the table and visualize hitting them, and then do so. Eventually you'll have the feel of any serve you can visualize in your head, and to repeat that serve you just have to match the feel of the serve that you've learned.