Stretching for tennis is very important! The most common injuries are rotator cuff tendinitis and “tennis elbow.”
Rotating Wrist Stretch. Place one arm straight out in front and parallel to the ground. Rotate your wrist down and outwards. Use the other hand to further rotate.
Kneeling Heel-down Achilles Stretch. Kneel on one foot and place your body weight over your knee. Keep your heel on the ground and lean forward.
Shoulder stretch. Cross one arm across your chest. Use your other arm to create a perpendicular angle and pull back.
This is just a starting point, but there is more benefit to using a wide variety of stretches!