This is a great drill that combines groundstrokes power, placement, and finesse.
The ball machine will feed balls deep to my left side; I will be alternating hitting series of 3 balls: 1 forehand groundstroke, 1 backhand groundstroke, and 1 drop-shot, aiming to the right side targets, then after awhile to the left side targets.
This exercise is very good for footwork, early preparation, conditioning, placement, finesse.
Also, this drill requires a constant change of grips between the forehand, backhand, and drop-shot strokes.

Technical aspects to follow:

Forehand groundstroke:
- grip: semi-western/eastern;
- early preparation with the racket head higher than the shoulder, elbows elevated, non-dominant hand cradles the racket neck to limit the backswing, big shoulder turn;
- open stance for deep balls, square stance for shorter ones;
- brush up on the back of the ball to create topspin.

Backhand groundstroke:
- grip: eastern backhand (one-handed), or continental (dominant) and eastern (non-dominant) for two-handed backhand;
- early preparation with the racket head higher than the shoulders, back elbow elevated;
- let the racket drop under the ball then swing from low to high to create topspin;
- separate the hands to keep the body in balance and sideways (one-handed), finish with the racket over the dominant shoulder for a two-handed backhand.

Drop-Shot:
- grip: continental/hammer
- prepare with the racket head higher than the eventual point of contact, 90-degree angle between the forearm and racket
- push the ball from high to low to create the slice/under-spin
- open the racket face at contact for extra spin.

Secrets:
- Forehand and backhand groundstrokes - trust the spin; keep the forearm and the grip relaxed.
- Drop-shot - avoid the backswing, cushion the ball at contact.