Hi,
Here is a link with some tips on making jumping hoop shots:
http://www.ehow.com/tips_8842.html
Do your school coaches know you sprain your ankles easily? If they do, this will be a disadvantage in making a team.
Have you talked with a Podiatrist or some other type of Doctor, like an Orthopedic Doctor about your feet? A Professional might have some suggestions as to what to wear, or do, to prevent the ankle sprains.
I do sincerely wish you the best.