One of the most common causes for the fact that people hit the ball with the heel of the club rather than in the center of the club is that they start at address in too slack a position. So that as everything extends out at impact the heel of the club runs out and gets in line with the center of the ball. What you want to do is that you want to get measured at address. I have a drill that I call the Kentucky drill because it will help you to get your setup correct for this. The abbreviation for Kentucky is KY, so what I would like you to do is to get set up where you position your body so that it looks like a reverse K. This would be where your left side is tall and your right side is indented away from the target. Then I would like you to setup and make your hands, arms and club all look like a lower case Y, where there is just a straight line from the left shoulder down to the head of the club and then the right hand and arm form the other end of the Y just like this. Then take that setup and then just stand whatever distance from the ball that would create getting the center of the club lined up with the center of the ball. This drill will take care of any slack you have in your setup that would cause your club to overextend on the downswing and cause the ball to be hit with the heel of the club.