This is a conditioning drill I learned from a top college coach that improves quickness and footwork for doubles net players.

The right-handed player waits at the center line in the deuce court service box. Coach has a stopwatch. At the command of "go," the player shuffles from the center of the service box to the inside alley line, and drops to the forehand volley position (stepping forward with the left leg), then returns to the center stripe and drops to the backhand volley position, and repeats until 30 seconds are up. Players should be able to do this 30 times in 30 seconds. Most won't, for quite a while.

Reverse this for left-handers.