Kat's got it right with the RICE. You want to keep the swelling down, and heat is BAD for that. S'ok after the initial inflamation though.
I've torn ligaments and cartilage. I was once told in an ER that I had sprained my knee, but done no serious damage. It turned out I had completely torn the ACL (anterior cruciate ligament), torn a bit of cartilage and wound up having surgery to replace the ACL and fix the cartilage. Jeri's basic advice: if it feels wobbly instead of stiff, get your doctor to torture you some more. Note that in my case, the diagnosis/assessment by the ER docs had absolutly nothing to do with the outcome - I just would have known about it earlier.