When guys in particular want some extra yards, they usually stand farther from the ball and really stretch out their arms. They feel more powerful in this extended position. But the reality is, they end up producing less swing speed and hitting a weak drive to the right. Let me explain.
The problem with extending your arms is, you get more bent over, and your weight moves out to your toes (below, left). When you swing from there, gravity pulls you out even farther, so you react by pulling up to save your balance. That causes the clubhead to swing across the line from out to in. You might hit a strong pull, but chance are, you're going to wipe across the ball and send it slicing.
A better approach if you want more distance is to set up to hit a draw. Start with your arms relaxed and hanging comfortably from your shoulders, then take a closed stance, with your feet, hips and shoulders aimed to the right of your target (below, right). Then try to swing out to the right and hit the inside part of the ball. Think of it like a big, sweeping forehand in tennis. You'll sling the club through and rotate your right arm over your left. That's a draw—and that's real power.
Keeping tension out of your arms at address sets up a free-flowing swing back and through. One good way to do this is to hover the club off the ground before you start (below). If you sole the clubhead behind the ball, you'll tend to push it into the turf, which tenses up the hand and arm muscles. With the club up, you can stay relaxed and sweep the ball off the tee. No better way to launch your driver.