There is always a tendency to swing at the ball faster when you are trying to win the point and slower when you are trying to keep the ball in play. Both of these things can contribute to a loss of timing and rhythm. I would recommend finding your "comfortable speed" for each shot and keeping it the same regardless of the intent.
Changing the direction, hitting the ball deeper or shorter, or just hitting with more or less spin can be enough to win the point. Staying with the same racquet speed on most of your shots will allow you to make contact with the ball in a similar spot and help you develop good timing. This will give you a much better chance of hitting three, four, or five balls in a row and force your opponent to match and exceed that.
This idea works well when you are serving. Keeping the speed of your swing the same will increase your chances of hitting your serve more solid and making a few serves in a row. You can use placement and spin to change things up, while maintaining good timing and rhythm on your serve.
Trust your "comfortable" speed and stick with it.
Steve Annacone, USPTA Elite Pro, is the Director of Annacone Tennis, www.annaconetennis.com and MyHamptonsPro, www.myhamptonspro.com throughout the Hamptons, NY. In addition, Steve and Miguel Coelho have introduced the JET (Junior Elite Tennis) program at the Tucson Jewish Community Center (Tucson, AZ) for high level players ages 8-18. Please contact Steve at email@example.com.