Whenever you have a shot which you can hit at knee level or below, AND, you opponent is behind you, then you should hit a pinch shot. In this video, Ben Croft shows how he drills his pinch shots.
This series of racquetball instructional videos by Malia Bailey teaches the basics needed to get started playing racquetball.
A racquetball forehand is really just a good throw of the racquet towards the front wall. The more elevation you can give your arm and elbow will determine how fast you can throw. Pay attention to the slow-motion throwing action of this champion stone skipper.
The key to controlling any rally in racquetball is to maintain the center court position. In this video, Ben Croft shows the correct position to hold on the court is about 1 foot behind the 5 foot encroachment line. If you try to move too far forwards to cover a pinch or kill shot, then you will get beat by an easier to achieve passing shot.
For more information on racquetball court positioning, take a look at the following posts: