Clean your oven
Clean your oven at least twice a year. Clean more often if you use your oven everyday.
Use the Self Clean feature
Using the self cleaning feature allows you to get the oven super hot to help burn off any residue. Only use this feature when you are home. Make sure to open up a window and power on your exhaust fan to help remove some of the heat. Once the cycle is up, allow the oven to cool down for about 5-6 hours and then wipe it down using a towel and some oven cleaner.
Clean your oven with natural products
If you would like to go the natural way, you can use some baking soda and white vinegar as a cleaning agent. To do so, you will need to make a baking soda paste. Pour some baking soda into a bowl and add only enough water to make it pasty. Use a paintbrush or a sponge to spread this paste onto the desired areas and let sit overnight or for about 12 hours. Next you get a spray bottle and fill it with vinegar. Use the sprayer to spray the areas that contain baking soda causing it to react and help clean the dirty surfaces. Now just wipe away the mess.
Word of advice
NEVER place foil on the oven racks or floor of oven. When covering the racks in an attempt to keep them clean, you are actually stopping the circulation of the heat and will affect cook times greatly. When covering the floor of the oven, this acts as a reflector in gas ovens. By doing this, it will ruin the porcelain finish because it reflects heat which causes it to chip and degrades faster.