Heel shots are caused because you either move the center of your plane out towards the ball during your swing or you start too close to the ball at address
If you tend to come up out of your stance and hit thin shots you can not only fix that but also increase your clubhead speed with this easy drill using a block of wood to place your toes on
A common fault in the set up is having your head down and chin too close to your chest, this drill will fix that and allow you to turn effectively and use your legs correctly in the swing