Remove any racks from the oven.
Dampen a paper towel or cloth and wipe up any loose material or crumbs inside the oven.
Scrape off any burnt on material with a metal spatula or similar tool, then wipe again with a damp paper towel or cloth. It's all right if you can't remove all of the burnt material.
Fill a bucket with warm water, dampen the Magic Eraser, and scrub the inside of the oven. Rinse the Magic Eraser out in the warm water as needed. Magic Erasers have a texture that helps them scrub, so it's not necessary to use any other cleaner or soap, but you can mix a little dish soap with the water in a bucket if you find that the oven isn't as clean as you would like.
Wipe down any oven racks with the wet Magic Eraser.
Spray a little ammonia or an ammonia-based cleaner on any remaining burned-on material. Leave it for several minutes. Scrub with the Magic Eraser and plenty of water, then rinse the Magic Eraser thoroughly.