One of the oldest tips in golf is to keep your left arm straight--collapsing the arm is a common fault (top photo). Unfortunately, that thought can lead to all sorts of tension. Instead of thinking about your left arm staying straight on the backswing, focus on keeping your swing wide. You do that by pushing the handle of the club away from your body with your right hand (bottom photo). Your left arm will straighten naturally, without tension.
As you swing to the top, you should feel the lifeline of your right hand pushing into your left thumb. This will give you plenty of width and allow you to create a powerful coil, provided you make a full shoulder turn. Pushing away with your right hand throughout the backswing will set up a powerful downswing and longer tee shots.
LEADBETTER, a Golf Digest Teaching Professional, runs 26 academies worldwide, including its headquarters at ChampionsGate, Fla.