A good player tends to react to the shot that was just hit by moving their feet prior to the next shot.
If the shot that they (or their partner) has hit is offensive, and/or hit well, movement forward happens prior to the opponent's response. If the shot is more defensive or not hit well, a step or two back allows the player to defend and get back into the point.
Moving in anticipation of the opponent's response is extremely important since the speed of the game has increased substantially these days. A step or two can make a big difference in the ability to cover the next shot.
Keep in mind that this also applies to your recovery when you are pulled towards the outside of the court. Recovering a step or two prior to the next shot being hit will greatly increase your chances of getting to the next shot.
Remember to adjust your court position in between shots so you are able to cover the most likely response from your opponent.
Steve Annacone, USPTA Elite Pro, is the Director of Annacone Tennis (http://www.annaconetennis.com) and MyHamptonsPro (http://www.myhamptonspro.com). For details on lessons and clinics throughout the Hamptons contact firstname.lastname@example.org or email@example.com or call 865-300-7323