A lot of people think you need to make a big shoulder turn on the backswing to hit solid, powerful tee shots. I disagree. A big backswing is not for everyone. Many golfers' swings get out of whack when they try to increase how far they go back. They get wild with the lower body or make a big over-the-top loop on the downswing because they've lost control.
Just like when you buy a new set of clubs, the distance you take the club back should be custom-fit to your body. And here's a great way to determine it: Kneel on a couple of towels, hold your driver like you're addressing a shot, and make a backswing (above). Because your lower body can't really assist in the motion, you'll have to rely on the muscles of your mid-back to rotate your torso. Those muscles around the thoracic spine will determine your backswing length. When you can't turn back any farther from your knees, that's your new, custom-made backswing.
Remember that spot when you stand up and swing for real. Make your backswing fit your body, and you'll start hitting better drives because the motion will have synchronicity and control.
Sean Foley is a Golf Digest Teaching Professional.