Most players look to see where their opponent hits the ball before deciding if they have to move or not. You'll be much faster if you assume you will have to move, and flex your knees in preparation for moving, even before you know which way you are moving. Since you should be moving to nearly every ball - how often does the opponent just happen to hit the ball right into your forehand or backhand pocket? - How fast you are able to do this makes a big difference. Assume you will have to move to every ball and you'll move much faster.