Put Safety First
If you are going to try to retrieve an item that has slipped into your garbage disposal, then you need to make sure that both the disposal switch is in the "Off" position and that you have turned off the power by moving the circuit breaker that powers the disposal into the "Off" position.
Gather Your Tools
Because you should never put your hand in the garbage disposal, you will need a few tools to help you dislodge the item. Put a battery-powered headlamp around your forehead and turn it on. If you do not have one of these, ask an assistant to hold a flashlight over the disposal. Point the beam into the disposal to see if you can find the item. If you do see it, grab a set of tongs, scissors, tweezers or needle-nose pliers. If you do not have any of these items, you can improvise with an eyelash curler, a chopstick or a fork. You need some kind of tool that will help you lift the item out of the disposal.
Retrieving the Item
Place your tool of choice into the disposal. Clip the sides of the pliers, tongs or scissors around the item -- such as a ring or necklace. Grip the item gently so as not to damage it. Carefully pull it up from the disposal.
What to Do If You Don't See Your Item
If you do not see your item in the garbage disposal, you will need to call a professional plumber, who will remove your garbage disposal system to retrieve the item. Do not try to do this yourself, as a garbage disposal system can be a complicated system to disassemble and re-assemble.