Here’s a tennis drill for good balance. I must stress that it is just a drill, and like all drills, it is only meant to help you practice one aspect of your game.
Place three stacked cones on your head, or alternatively a folded towel, and do shadow strokes while trying to maintain perfect balance. You’ll find the only way you can hit multiple strokes while maintaining the cone position is to keep your legs nice and bent, and your head upright.
Any kind of jumping up and down before, during, or after the shot will cause them to fall immediately.
Of course this is not how you want to hit the ball in a rally – your movement will be more dynamic and you will change direction quickly. But the purpose of this drill is primarily to increase your awareness of your balance as you move, and as you hit.
Here’s a sample: