When faced with a buried lie in the bunker you must create a concussion in the sand in order to drive the ball up out of the bunker
To promote clubface rotation make sure your left hand grip is turned back enough and then take half swing concentrating on the rotation of your forearms
Start with a neutral grip making sure that your left hand is not turned over or under the shaft, this will prevent you from manipulation the clubface at the top of the backswing