The New York Times cites a new study on balance training and its positive effect on ankle rehabilitation, and consequently ankle injury prevention:
A major review published last year found that six weeks of balance training, begun soon after a first ankle sprain, substantially reduced the risk of a recurrence. The training also lessened, at least somewhat, the chances of suffering a first sprain at all.
The article mentions standing on one leg and stabilizing so you are not shaking on your foot. However, to improve the rehabilitation of an ankle sprain, write the alphabet with the other leg.
Stand on one leg and use the other foot to write the alphabet in the air. Exaggerate the movements with your toes to flex and extend your ankle as much as possible.
While improving balance has been shown to reduce the likelihood of another ankle sprain, you also want to regain the full range of motion. Writing the alphabet and forcing your foot through the full range of motion breaks down scar tissue and improves ankle flexibility.
Many times, players forget this aspect of rehabilitation and return to the court with reduced flexion in their ankle which detracts from the skill performance.