For the basic bunker shot you need to have a firm footing so shuffle both feet into the sand and this will also gauge how heavy the sand is.
Set–up with a slightly wider stance than normal stance as this will lower your centre of gravity to enable the clubhead to pass into the sand under the ball.
Position the ball towards your left heel with your weight on your left side and make sure that it remains there throughout the entire swing.
Your clubface should be slightly opened but aligned to the flag. Opening the clubface will allow the bounce (bottom of the sand iron) to be used correctly as it is designed to.
Your stance (feet, knees, hips and shoulders) should be aiming in an open position (left) of the flag.
The two photos below show the clubface slightly opened and the other more open if requiring more height.
Keeping your weight on the left side, cock your wrists and swing your hands up just below right shoulder height.
The clubhead will be picked up quite steeply which will allow for a steep angle of attack as the clubhead enters the sand about two inches behind the ball.
Make sure you keep turning your body through to the finish as this will allow the clubhead to continue through the sand preventing stopping on the shot resulting with the ball staying in the bunker.
It is important that the clubface remains open until well after you have contacted the sand whereby the hands may then tend to roll over.