When you find your ball under the lip of a bunker, or when you have little green to work with, the instinct can be to try and help it up in the air. Unfortunately, this often creates the opposite effect – a thin contact which send the ball out low, either failing to leave the sand, hitting the front of the bunker, or whizzing across the green.
Instead, setup with the ball slightly forward in your stance and open the clubface slightly. When you make your swing, feel the club pulling through towards your left pocket with speed. This will force the club down into the sand and make it cut under the ball, popping it up quickly.