Commercial oven cleaners work, but the fumes are rough in a closed kitchen. Baking soda and water do almost the same job if you give them time. The trick is to apply it at night and wipe it out in the morning.

Put the racks in the bathtub on an old towel (to protect the tub), cover them with the hottest tap water you have, and add a generous squirt of dish soap or a half cup of baking soda. Soak overnight, then scrub with a stiff brush and rinse. Check your manual before putting racks through a self-clean cycle; many will discolor or lose their slide.
Make a thicker baking soda paste and spread it on the inside of the glass. Leave it 20 to 30 minutes, then wipe it off with a damp cloth and buff dry. For grease trapped between the glass panes, check your manual; on many ovens the door can be removed and the inner panel accessed.
The self-clean setting heats the oven to around 900°F and burns residue to ash. It works, but:
Put a sheet pan on the rack below anything that might bubble over. If something spills, sprinkle salt or baking soda on it while the oven is still warm (not hot) so it's easier to wipe up later. A quick wipe once a month means you'll rarely need the overnight method. See our appliance care guide and kitchen cleaning tips for the rest of the kitchen.
Mix about half a cup of baking soda with a few tablespoons of water into a paste, spread it inside the cool oven, avoiding heating elements, and leave it overnight. Scrape it out, spray any residue with vinegar and wipe clean.
Soak them overnight in a bathtub lined with an old towel, in hot water with dish soap or baking soda, then scrub with a stiff brush and rinse.
Generally yes, but remove the racks unless the manual allows them, ventilate the kitchen, never leave the house while it runs, and keep pet birds out of the house because the fumes can harm them.
Wipe up spills when the oven cools and do a full cleaning every three to six months, depending on how much you cook.