The paper washer packed under the flange in most disposals goes under the sink. These items keep the disposal snug against the sink, preventing leaks and reducing vibration while the unit is running. Run the disposal each time you put something into it. Cheaper models, which do not contain many or any stainless steel components, are susceptible to corrosion from food waste left sitting inside. Use cold water when the disposal is running and for a minute or two afterward.
Cool water helps make fatty substances form solids, which are easier to grind.
Running water afterward ensures that particles will be flushed through the system. Put coffee grounds into the disposal. Their abrasive texture helps clean the grind chamber. Some manufacturers recommend grinding small bones to keep the grind chamber clean, but experts disagree on whether doing so increases the likelihood of clogged plumbing. Keep a wrench handy to loosen jammed disposals.