I recently bought a jump rope, and while I haven't gotten around to properly exercising with it, I did a few test runs to test the length. Each time I would jump about 30 seconds or so.
I've noticed that when I jump, I eventually bang my ankle bones together (the medial malleolus, to be accurate), which kinda hurts, and definitely indicative of bad form. I've tried to jump in place, without the rope, to see what kind of form I have, and that happens again, even if I try to keep my feet together while jumping. This happens even if I jump short and controlled jumps (but also with the bad-form tuck-your-feet-back-higher-jumps that I definitely plan to work against).
(I should probably also say that I never used a jump rope before; I'm pretty thin, if that matters.)
What can I do to correct my form, and what kind of problem is this indicative of?