First and foremost, garbage disposals are designed to grind up small amounts of residual food left on plates, pots and pans after a meal. If you use it for anything more than the above description, you are asking for trouble. Use a garbage can to dispose of larger quantities of old food. Disposal problems are one of the most common residential plumbing calls received by local plumbing companies.
Never put stringy, fibrous materials like celery down a disposal. Never put more than a few grains of rice or a few pieces of pasta at a time. These swell up and contribute to clogs. Contrary to urban myths, you should never put egg shells down a disposal, they do not "sharpen the blades." The heavy shells sit in your pipes and contribute to clogs.
A Roto-Rooter plumber in Phoenix once told me about a sink so full of rice that he had to use a screwdriver like a chisel to remove the hardened mass and restore water flow down the drain.
Garbage disposal calls are one of the most common kitchen plumbing jobs handled by plumbing companies and most of the problems could have been easily prevented with a little bit of common sense.