Each time you hit a shot, you must recover. The "old school" idea is to get back to the middle of the court. However, in modern tennis you are better off thinking that you are going to move in the direction of the open court as soon as you are finished with your follow through.
This is true both at the baseline and at the net. You may need to follow the ball a bit more when you are closer in so make that adjustment if you are at the net. In addition, if you are like most players and would rather hit your forehand as opposed to your backhand, position yourself slightly towards your backhand side of the court (not the middle) and look to move to the forehand right after your opponent makes contact with the ball.
Keep in mind that the further you are off the court, the more you want to cover the opening and force your opponent to hit the ball behind you. The better players will do this if they see you are covering the opening well, but it is a much more difficult shot to execute since the area of the court they are hitting to is smaller.
Remind yourself that all of your shots are coming back and that you need to recover and expect to hit another ball regardless of how good or bad your shot was hit. How well you recover can determine your level of success in the match.
Steve Annacone, USPTA Elite Pro, is the Director of Annacone Tennis (http://www.annaconetennis.com) and MyHamptonsPro based in Sag Harbor, NY (http://www. myhamptonspro.com) and Tennis Professional at Ventana Canyon Golf and Racquet Club in Tucson, AZ. For details on lessons, clinics, or coaching, contact Steve at email@example.com or call 865-300-7323