With some simple tweaks, you’ll be able to accelerate your service speed. Begin by relaxing, breathing deeply and loosening up your muscles. If you are trying to muscle your serve in, the resulting tightness will slow you down.
Stand at the baseline with your chest facing the side fence, not the net. Relax your racket, wrist, arm and body.
Use a continental grip. This means most of your hand is directly on top of the racket handle while the face of the racket is parallel to the side fence. Imagine holding a hammer.
Begin your serve using a motion similar to tossing a tennis ball up the sky with your palm facing upward.
Be sure to take a full swinging motion to allow your racket to drop behind your back before launching it upward to meet the ball. Now move racket upward on its edge, rotate your wrist and forearm so the strings face the ball.
With contact almost directly overhead, straighten (snap) your wrist to meet the ball and then relax the racket, wrist and arm to finish the follow through. This wrist snap, along with a relaxed and full swing, is key to creating a faster serve.