Baking soda and vinegar works really well. I just went to look it up again as I was not sure if you spritz it first with hot water or use vinegar first. Mix some hot water and baking soda until you have a pliable paste. Spritz the oven with hot water then apply your paste and let sit overnight...I have done less than overnight before but you tend to need a bit more elbow power to loosen tough stains, afterwards dampen the baking soda again (as it will be dried at this point), wipe the baking soda from the oven then spritz clean residue with vinegar on a cloth.
If there are really tough stains left I've actually applied baking soda to them with vinegar on top to create a bit more fizzing power action to the stain, once it quits fizzing I use a metal spatula to scrape it away then wipe down clean.