Approximately 10-20%1 of waste is composed of food. Garbage disposals effectively reduces the food waste to a liquid mixture, which is easier to dispose since there is already an infrastructure in place for liquid waste.
Blades powered by an electric motor grind the food up to small bits. The resulting mixture should be approximately 70% and 30% food. In order to accomplish this balance, the water must be running while using the garbage disposal.
Avoid putting items that will mess up the blades or create a clog in the garbage disposal. These items include, but are not limited to:
Dump 2 cups of ice cubes, ¼ cup of vinegar, and some lemon peels into the garbage disposal. Turn on the garbage disposal to start grinding up the mixture. When the ice cubes are almost completely ground up, start running the faucet to help wash everything down. The ice cubes will help sharpen the blades and knock loose food that is stuck. The vinegar and lemon peels will clean and leave a nice smell. Add baking soda to the mix if any smells persist.
An easier way to perform this maintenance task is to create an ice cube mixture. Make a solution of three parts water and one part vinegar and pour into an ice cube tray. Cut up a lemon and put a small piece into each ice cube slot. After freezing completely, dump the ice cubes into the garbage disposal and grind them up completely. Turn the faucet on when the ice cubes are almost completely ground up.
Be sure to mark the ice cube tray and keep it dedicated for this maintenance task. The vinegar smell won't come out easily so it will be unpleasant for normal use.
1 - http://www.epa.gov/osw/nonhaz/municipal/pubs/msw2009rpt.pdf