Some rehabilitation exercises for a sprained ankle would be:
Towel stretch. Sit with your leg straight in front of you. Place a rolled towel under the ball of your foot, holding the towel at both ends. Gently pull the towel toward you while keeping your knee straight. Hold this position for 15 to 30 seconds, and repeat 2 to 4 times. In moderate to severe ankle sprains, it may be too painful at first to pull your toes far enough to feel a stretch in your calf. Use caution, and let pain be your guide.
Towel curls. While sitting, place your foot on a towel on the floor and scrunch the towel toward you with your toes. Then, also using your toes, push the towel away from you. Make this exercise more challenging by placing a weighted object, such as a soup can, on the other end of the towel.
