This is simply the best groundstroke drill I've ever used. I learned it from a great college coach about 8 years ago, and it has helped me correct many different problems: footwork, racquet prep, height and speed, and it helps a player increase depth. However, prepare to get pegged when your player tires - I have the bruises to show for it.

Player stands just behind the baseline at the center hashmark. You kneel about 6 feet in front, off to the side with a 60-ball hopper. Toss low balls to the player: your toss should be less than two feet high, and dead balls work best. Player shuffles, catches ball on the rise and shuffles back to the hashmark. Repeat until the hopper is empty, varying placement from standard feed, to wide, to at the body. As the player tires, it's important to remind her to get her racquet back early, bend her knees, and to keep her back straight.

Surprisingly, my players love this drill - it's exhausting for them, especially on the backhand side, which requires more steps. Only once in 8 years has a player hit all 60 balls in. She went on to play #1 at a D-1 school.