Coming up out of posture during the downswing is a common fault created by a lack of strength in the glutes (buttocks), try stretching and strengthening them by lying on the ground with your knees bent and lifting your hips and buttocks off the ground for ten seconds
Keeping your right hand on the grip in a neutral positoin allows the clubface to come into impact square, turning that hand in either direction will cause the face to close or open at the top of the backswing
Your impact should start right at the ball and the lowest point of the divot should be ahead of impact, use this bunker drill to practice impact to develop consistent shots