The two most common bunker problems are allowing your club to hit the ball instead of using the sand as a cushion and allowing your spine or stance to tilt back which causes the club to enter the sand too early
Your ball positon should match the low point of your swing, so it changes with each club and depending on whether you want to hit the ball regular or with a special shot like a draw or fade
Learn the process of developing a good golf swing and practice swinging