Watch the ball hit the strings
If you find that you are hitting your ground strokes long or into the net, then the first thing you want to check is if you are watching the ball long enough.
Concentrate on seeing the ball actually hitting the strings. This will help you to hit the ball in front and force your eyes to stay on the ball. The most common error is the head lifting off a stroke a little early, to look at the target. Focusing intently on the ball will help prevent that from happening.
When you train, practice watching the ball onto the strings and this will teach you to watch the ball long enough, especially when under pressure. Remember - it is rare at full speed on ground strokes to see the ball actually hit the strings, but attempting to do so will help you to keep your head still, which is a fundamental key to consistency.
If you are hitting your shots too short, make sure that you hit with more height. (see forehand video for water level) If you still find that you do not have enough penetration, then after every shot, try to move one step behind the ball after contact, which will cause your body weight to be behind the ball more and should improve your length and weight of shot.
If you find that you are hitting the ball long, but hitting it well, try to make sure that you are not just leaning back slightly, as you hit the ball. The other reason for this, is that you are not hitting with enough topspin.
Spin and angles
Adjust your topspin, by just coming from 'under the water' (see "Forehand" video) and turning the wrist over a little faster. If you are netting, make sure that you are not hitting the ball too flat. Lift the ball by getting 'under the water' and play with topspin. If you find you are netting but with topspin, you are probably not going deep enough into the water, or you are turning your wrist over a little too fast.
If you find that you are not getting enough angle on your cross-courts, think about hitting a little more on the side of the ball. This will cause you to hit the ball a little more in front and give you more angles.
It is quite normal to suddenly hit the ball a little wide, but it is always easier to hit the ball and then pull it back a little. Rather than trying to edge it out slowly, just exaggerate for one or two shots and you will soon find your measurement.
If you are floating your backhand slice and not getting any penetration, make sure your wrist is firm enough. If you have very little penetration, or finding it difficult to hit the slice backhand, put more weight onto the front leg. In other words, lean into the ball. If you find you are losing control of the slice backhand, it is probably because you are dropping the racket head, rather than gliding it along the table or firmly across the back of the ball (see backhand video).
by David Sammel