There are two categories of racquetball shots. The first group are shots which move your opponent from the front of the court to the back of the court. These shots include ceiling balls and passing shots. Passing shots can be hit either down the line or cross-court. Again, your intent is to move your opponent from their center court position into the back court area. Your goal is to move up into center court position.
The second group of shots are meant to end the rally. End of rally shots include kill shots and pinch shots (a pinch shot is hit low into a front corner). If done correctly, an end of rally shot will bounce twice in the front of the court before your opponent can get to it.
So a good rule of thumb is to hit ceiling balls and passing shots when your opponent is in front of you. And if you are in front of your opponent, and can hit the ball at knee level, then hit a pinch or kill shot.