It’s important to warm-up before playing tennis with dynamic stretching and to cool down after with static stretching.
Dynamic Stretching involves movement-based stretches. One of my favorites are arm circles. Stand with your feet shoulder-width apart and arms in the Leonardo Da Vinci Vitruvian Man pose. Start with small, tiny circles, then slowly increase until doing a full windmill rotation with your arms from the shoulders. Reverse the direction, staying big, then shrinking the circles back to tiny before stopping. This should take 30 seconds to 1 minute. Jogging around the court slowly, running the lines, and Little Orphan Annie knee circles are also wonderful dynamic stretches. You should avoid traditional, static stretching before exercise because it increases the likelihood of a muscle tear either during play or because you are extending cold muscles too far without warming them up properly. If you don’t believe that static stretching is passe and dangerous, read this New York Times article from Halloween 2008 entitled, “Stretching: The Truth.” Here are some great dynamic stretching visual links: