There are four sources of power in your swing: the wrists, the arms, the pivot and your ability to syncronize and time the movements
A common error with beginner golfers is to get your left hand grip too much underneath the club, engrain the correct left hand position in the grip with the simple drill
Put a plastic ball between your knees in order to take your backswing with your torso rotating more than your hips, disassociating the lower body from the upper body and creating more power in your swing