Study more, not-study less. Not to say you can't have fun, just be efficient when it IS study time.
That's about 70% of it. In basic sciences I'd say the other 30% is finding something that works for you and doing it as hard as you can. There are always those loud people out there who say, "I do such and such to study and I do great, my way is TOTALLY the best way to study;" just tune those people out and go about your own business without getting freaked out about how other people approach the same problem.
In clinics, yeah, the other 30% is knowing your patients really well and looking good when you present to the attending. At my school residents evaluate us too, so it's also important to be a team player (not that you shouldn't do that anyways to, ya know, not be a d-bag).