While there are many chemical over cleaners, here's a method to clean your oven using natural items.
Run the oven's self-clean cycle if it has one. Begin by setting your oven to 125 degrees F. Once it is at the correct temperature, begin to pour sea salt lightly on the areas that have residue and grime. If those areas are completely dry, then you must moisturize them a little with filtered water in a spray bottle; spray each dry area once or twice before applying the salt.
Turn the oven off and let it cool down completely. Then take a scraping device, preferably a plastic one that will not leave marks in the oven, to scrape off the dirty areas. Take a towel and wipe up the crusted residue as you are scraping it away. Once this is done, take a damp sponge and wipe down all the affected areas, paying special attention to wash out all of the salt residue so it does not crystallize and become residue on its own.
If this does not provide significant enough cleaning power, then you should spray the affected areas with a mix of water and vinegar several times. You can use a little bit of lemon juice to counteract the smell and add a little bit more cleaning power. Sprinkle baking soda conservatively over all the moistened areas. This will create a chemical reaction if the vinegar was used.
Begin scrubbing these areas gently with a very fine steel wool until the areas are fully clean. Wipe off all the remaining grime with a dry towel. Wet a sponge and go over the areas again to get all the remaining vinegar and baking soda out of the oven. Once you have finished, it is advisable to run the oven's self-cleaning cycle once more.
Try to use both of these methods in concert for maximum effect, but try to use the water and salt method first. You may want to try these methods once a month as a preventative measure against excessive build-up or malfunction with the device. If you cleaning an industrial sized oven used in commercial operations, you may want to do this once a week.