When I've done them in the past, I cleaned them with brake cleaner first. Then, I used a rotary tool to clean off the baked on crap. Then, lightly sand, and clean again. I'd recommend using a hi-temp primer too. You can find stuff at PepBoys that dries in 30 minutes. And, I agree -- bake it in the oven for a while once you get the final coat on. It will help prevent it from peeling.
