Disconnect the Power
Anytime you are working with a garbage disposal, turn off the disposal and disconnect the power at your circuit breaker to ensure that the disposal cannot come to life while you are working on it.
Protect Yourself
If you are working with a glass or ceramic cup, the likelihood of hurting yourself is greater than if you are working with a plastic cup. Protect yourself by wearing thick work gloves and a pair of goggles.
Lifting the Cup
Try lifting the cup out of the drain using a pair of needle-nose pliers. Do not grip too firmly if you are trying to dislodge a glass cup. Ask a helper to hold a flashlight over the disposal so that you can see as you try to pick up the cup. If you do not have a helper, wear a headlamp. Gently pull the cup to the surface of the disposal with the pliers.
Water Trick
Fill your sink with hot water and a little soap. Place a toilet plunger over the disposal, ensuring that the plunger forms a seal over the disposal opening. Plunge the disposal up and down until the cup loosens in the disposal and pops up.