No matter how long or short your swing, one fundamental you need to apply is keeping your arms "connected" to your body as you swing back and through. If you do it right, you're making it way easier to have good timing during the swing and to move the club on the correct plane.
It's easy to see when your lead arm "disconnects" by moving away from your body on the backswing. But the trail arm pulling back behind you causes just as many problems. Either way, your swing gets shifted off plane, and you'll have a hard time getting your body, hands and arms to work together on the downswing.
Ideally, your lead arm moves up your chest in the backswing, and your trail arm doesn't do much more than fold up from the elbow and rotate out slightly. It's a simple move, but you have to do it in addition to turning your body. Remember, the arms bring the club up, and the body rotation brings it around. Get it right, and you'll be in sync, with the club moving on plane.
Your trail arm should bend up at the elbow and move slightly outward—not get trapped behind your body.
Hank Haney is based at the Hank Haney Golf Ranch in Lewisville, Texas. To get fixed in Golf Digest, send Hank your swing on Twitter: @HankHaney.