Many players have a tendency to swing from their elbow rather
than their shoulder, which can cause problems later as they
improve. A good hip rotation and swing from the shoulder
allows the racquet to stay online behind the ball much longer
than with a swing from the elbow. In addition, swinging from
the shoulder allows a longer follow through, which will
eventually allow you to add more power and spin to your shot.
Make sure that when you are pulling the racquet back, you do
so with the shoulder as well. If your elbow looks like it is
touching your ribs, you will probably swing around your body
and cause you to loose valuable control. A big backswing is
not necessary but a fluid stroke begins with good racquet
preparation, taking the racquet back in one piece with the
shoulder and a good hip turn. Swinging from the shoulder will
also allow you to follow through up above your opposite shoulder
rather than a low swing under your arm.
The same idea holds true on both the forehand and
backhand. A quick flick of the elbow or wrist, although adding
power, can completely destroy any control you might have. The
more moving parts there are in your swing the greater the chance
that one can go wrong. Of course I'm not suggesting that you be
completely stiff and unnatural. However, I do see that many
players lose points because they have too much in their swing
rather than too little.
Think of the hinges on a door and make your shoulder the hinge
of your swing. You will have more control, the ability to have
more power, and you probably won't have as good of a chance of
having tennis elbow.