if you don't have a self-cleaning oven.. i don't, but know several people who do,,, then use oven cleaner. spray the whole thing, wait an hour or two and then wipe. Easy as cleaning mirrors (just a lot grosser)

I recently moved, and when I cleaned the oven, which hadn't been cleaned since we moved in three years prior, that is what I did and it came out sparkley, no scrubbing needed. it was really gross though. haha.