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
Advanced player looking to add more width on their backswing and improve their left arm position should try this neat little drill from Vijay and put a headcover under their right arm
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