Following an ankle sprain, strengthening exercises should be performed once you can bear weight comfortably and your range of motion is near full. There are several types of strengthening exercises. The easiest to begin with are isometric exercises that you do by pushing against a fixed object with your ankle. Once this has been mastered, you can progress to isotonic exercises, which involve using your ankle's range of motion against some form of resistance. The photos below show isotonic exercises performed with a resistance band, which you can get from your local therapist or a sporting goods store.