The shoulder shimmy is done by thrusting one shoulder forward while pulling the other shoulder back. Do not think of it as shaking your boobs, but as shaking your shoulders (the breasts will come along for the ride).
Shoulder Thrust Forward
This move is done by pushing just the shoulder and only one shoulder at a time, forward.
Shoulder Thrust Backward
This move is done by pulling just the shoulder and only one shoulder at a time, backward.
Shoulder Lift
This move is done by pulling just the shoulder and only one shoulder at a time, up. Practice by lifting your shoulders as if saying "I don't know", then try just one at a time
Shoulder Drop
This move is done by dropping just the shoulder and only one shoulder at a time, down. This will be the opposite of lifting; you will want to lift your shoulders up first and then drop them down.