According to Ben Croft, the most important shot in racquetball is the serve. He also talks about changing his pattern of serving straight-in drive and lob serves by mixing in Z-drive and high Z-lob serves.
The serve is the most important aspect of racquetball. You have complete control of the speed, angle, height and direction of your serve. Your goal is to either ace the serve or force a weak return of serve.
Shane Vanderson discusses how top racquetball players will constantly vary the height, speed, and angle of their serves. This strategy will keep their opponent off-balance and prevent the serve from becoming predictable.