All squash players say "watch the ball". But, did you know that there is a certain way of watching the ball? During a rally your opponent will be either in front, behind, or parallel to you. There is only one way to watch in each of these circumstances.
When your opponent is in front of you, it is easy to see where and when your opponent is going to hit the ball. The secret is to stay as close to your opponent as possible, without crowding, as he or she is striking the ball. This adds mental pressure to your opponent because by doing this your opponent knows you're ready, especially for a drop. If your opponent is in front, remember the drop is the most likely shot to be executed. And this means trouble. So get close to your opponent when he or she is in front of you.
When your opponent is next to you or behind you, try not to look directly at the ball. Use your peripheral vision. The reason to do this is that it may be physically impossible to follow a fast crosscourt and turn your head at the same time. Follow the ball with your eye to the service line and then lock your eye at the serve line area and let your peripheral vision track the ball to your opponent's racket. The only exception is if you've hit a high length shot that comes off high on the back wall. In this instance you need to watch your opponent closely. Just make sure you're watching from the front while on the "T".