Ok this isn't so much a coaching tip and more of a bit of advice for your well being. Over the years I have seen many cases of tennis elbow (or lateral epicondylitis as it is technically known). And it doesn't just affect your tennis - it affects your routine daily life from knocking in a nail to ironing your clothes. So what is tennis elbow. Well if you hold you playing arm out with your palm facing downwards and then put your on playing hand on top of your elbow, then clench and un-clench your fist you should be able to feel the muscles on your elbow tensing and un-tensing. This is the area where tennis elbow occurs. So if you are playing and you feel a pain or an ache in that area of your elbow STOP. Seek advice. It can be caused by poor technique especially on the backhand, or maybe a racket grip that is too small, or simply holding the racket too tightly. But whatever, don't wait till its too late because once you get it, it is a devil to get rid of.
It is really important that you can control what spin you put on the ball whether it be slice or topspin. I hear you ask 'Who cares which way the ball is spinning as long I get the damn thing in'. Controlling the spin will allow you to dictate the point better and give you more purpose behind the shot. So why topspin? Well topspin will allow you to hit the ball harder and still get it in. Not wishing this to be a physics lesson (I was useless at physics - just thought I'd throw that in) the spin will make the ball arc over the net giving you more clearance over the net and make it dip quickly the other side. Also it will make the ball kick the other side making it more difficult for your opponent. So how do you produce it? It is important to drop the racket below the intended contact point. Then, and this is the important bit, with the racket face facing the net you need to brush up the back of the ball and finish you swing up over your shoulder. Contact point should be no higher than waist high. Now have a look at the rotation of the ball as it goes over the net. Is it going end over end. Yes? Perfect! No? Try again. Once you master it, it will change your game.