When working with students on their serves, I like to stress accuracy, placement and control before power. I set up targets in the service box, (left, middle and right). I ask the student to hit five serves at each target area. Since the objective is to work on their control, I only allow them to hit the ball at approximately 70% of their full power. Next, I give them permission to hit, for example, a first serve (more flat than spin) at the left target at 70% of full power. Then, I might say "try to hit a second serve (more spin than flat) at the right target at 70% of full power.
Once they can handle my varied instructions, I let them start telling me what they are going to do -- either a first or second serve (at 70% of full power) and the direction on the serve. Only after they seem to accomplish these tasks reliably at 70% of full power do I add the challenge of letting them hit some serves occasionally at 90% of full power."
When the student is finished, he or she has mastered accuracy, placement and control -- before trying to add power. Once the student understands that their success with serving depends mainly on what they do with their serve at 70% of full power, not at 90% of full power, then the lesson is learned. Trying to hit at 90% of full power only a small percentage of the time will keep your opponent off guard, allowing you to hit most of your serves at 70% of full power. At 70%, you will have more accuracy, better placement and control. Also, do not forget to vary hitting both your first and second serves at 70% and 90% of full power. This strategy will also help the server who tries to over hit their first serve and gets a low percentage in and then under hits their second serve and gets killed with it.
I wish everyone a great 1999! Let's use this year to get in shape for the MILLENNIUM!
Good Luck on the Court!