Some heel shots are caused because at set up you are too close to the ball causing your arms to start inside your shoulders
Practice your entire swing in super slow motion, this will allow your mind to focus on the correct muscle movements needed instead of trying to make your brain work on the correct movement while you are swinging, just do it don't think it
Proper impact is by far the most important part of the golf swing, you must make contact with the ball and the ground at the same time with a square clubface in order to maximize your distance and accuracy