When I was growing up, we were always taught to keep the ball deep. The idea was to push your opponent back and give them very few opportunities to move forward.
These days, there are a lot of players who start the point standing relatively deep in the court. This pretty much negates the "hit the ball deep" idea. Actually, if you hit the ball deep against these players, their shots are likely to get you in trouble and on the run. Try varying the depth of your shots—hit some short balls to start the point and try to pull the player in. If they don't follow your shot to the net, follow the short ones with some deep balls.
Mix in a medium depth ball with some angle, and you now have the player moving side-to-side, and up and back. This makes the court seem bigger and also puts some doubt in your opponent's mind about where to stand and where they will have to move. The intentional short ball works very well against the players who return serve from way back and can often force them to pop up the ball.
A short serve is also an excellent way to make your opponent feel uncomfortable if they are standing many feet behind the baseline to return serve. Again, mix up the depth of your serve so the opponent has to do more than just move side to side. Pushing and pulling the player back and up can be as good, or better, than just trying to run them back and forth behind the baseline.
Steve Annacone, USPTA Elite Pro, is the Director of Annacone Tennis, www.annaconetennis.com and MyHamptonsPro, www.myhamptonspro.com throughout the Hamptons, NY. In addition, Steve and Miguel Coelho have introduced the JET (Junior Elite Tennis) program at the Tucson Jewish Community Center (Tucson, AZ) for high level players ages 8-18. Please contact Steve at email@example.com