"The key to this drill is to exaggerate your technique.
Get your weight going forward into the ball, keeping your head over your front knee at all times. Ask the batsman what length they find comfortable to drive the ball. Drop the tennis ball on that length, and on the second bounce, step in to the ball and play your drive shot.
The key points are: Keep your head forward, into the ball, and over your front knee. Your front foot needs to be right next to the pitch of the ball. And keep your hands going through your target line."