Clean your disposal by putting ice cubes and 1/4 cup of white vinegar into the unit and operating it with no running water. As the blades grind up the ice, it removes food particles and gooey build-ups. When it sounds like the cubes are all gone, start a slow trickle of cold water. You will probably find that the disposal's drain openings are frozen and clogged with ice, and the water will start to back up -- which is good -- because the churning water also washes the sides before the ice melts, the drain clears, and everything drains away.
For a more thorough cleaning, sprinkle some baking soda on top of the ice cubes. To make the disposal smell fresh, add some citic acid crystals, Tang or a drink mix containing Vitamin C, or half a lemon.
You can also use vinegar ice cubes as an easy means of cleaning your disposal and sharpening its blades. Pour 1 cup of vinegar into an empty ice cube tray and fill the balance of the tray with water. Put the tray in the freezer until you have solid vinegar ice cubes. Periodically pour an entire tray of ice cubes into the disposal while it is running. Just be sure to mark the tray with the vinegar ice cubes. Otherwise your guests will have an unpleasant experience next time you serve them a cold beverage.