I've seen a lot of goofy "demonstrations" from shoulder swings to the spread eagle from players out on the court getting warmed up just before a match.

Some of the things I've seen can be effective if you know the precise "feeling" you should be trying to accomplish during the stretch, but NOTHING will loosen your rotator cuffs before a match quite like this - and you can do it on the court with nothing but a Tennis Racquet:

Rotator Cuff Stretch #1:

1) Extend your (right) upper arm directly out to the side grasping the handle with your palm

2) With the racquet face towards the ground, reach across the front of your body with your left arm and gently full forward

** Make sure you keep your upper arm of the shoulder being stretched parallel to the ground through the entire movement for an effective stretch. Be careful not to stretch in a ballistic or uncontrolled manner. Ease into the stretch.

Rotator Cuff Stretch #2:

1) Extend your (right) upper arm directly out to the side grasping the handle with your palm

2) With the racquet face towards the sky, reach across the front of your body with your left arm and gently full forward

** Make sure you keep your upper arm of the shoulder being stretched parallel to the ground through the entire movement for an effective stretch. Be careful not to stretch in a ballistic or uncontrolled manner. Ease into the stretch.