Remove the racks from your oven and take them to an area where you can make a mess without causing problems for yourself later on. Outdoors, the garage or in the utility sink or bathtub are all good options.
Use a butter knife, spoon or scouring pad to scrape baked-on food off of the oven racks and out of the oven itself. Remove as much of the excess mess as you can by scraping it off. Rinse the racks with water when done.
Spray down the interior of the oven and the racks with an oven cleaner of your choice. You can either use commercial oven cleaners or make an oven cleaner yourself by combining a 1/4 cup of baking soda, a spoonful of liquid dish detergent and either water or vinegar to make a paste that you can then apply to the areas of your oven and oven racks that need to be cleaned. Let the baking soda paste sit for several hours before scrubbing. If you use a commercial oven-cleaning product, you need to follow the instructions for the product, which typically involve heating the oven up, spraying it down, then letting it sit overnight so you can wipe the mess out of the oven the next morning.
Scrub the oven clean using a damp sponge. Use the abrasive side of the sponge on any remaining baked on grime. Wipe the oven down completely with a clean sponge to ensure grime and cleaning products are removed from the oven before you use it again.