Preferably use an oyster knife, which is a stiff pointy knife with dull sides. The dull sides help to prevent you from cutting yourself if you slip. A table knife will not work–the oyster knife must be very stiff in order to give you leverage to pry open the shell. Many kitchen supply stores and supermarkets sell cheap oyster knives.

It is also helpful to have a thick glove, preferably made of kevlar (for your left hand if you are right-handed or a glove for your right hand if you are left-handed) to help prevent injuries if your knife slips.

1. Insert the tip of the oyster knife into the bottom v-shaped hinge of the oyster where the two shells meet. Wiggle the knife to wedge it deeper and to find the weak point of the hinge.
2. Give the knife a few sturdy pushes into the shell. If you have found the weak point than the top shell will loosen. If not, then keep wiggling and pushing the knife until the top shell dislodges.
3. The oyster has a muscle which connects it to the top and bottom shell. Run the side of the knife up across the top of the shell to disconnect the muscle. Remove the top shell, and then use the side of the knife to disconnect it from the bottom shell. Be careful not to spill the juices.

The pictures below are from Tomales Bay Oyster Company picnic benches.