The driver is unlike all the other clubs in your bag—you really don’t want to hit down on the ball at all. In fact, the average Angle of Attack (AoA) on the PGA Tour is 1.2 downward, but Rory McIlroy hits up 2-3 degrees and Bubba Watson hits up 5 degrees and they KILL it! The AoA is simply a measurement of whether the club head is moving upward or downward through impact. 
In the photo, my student is working on the Towel Drill to help him stop hitting down on the ball. The driver doesn’t work well when you’re hitting down on the ball with it—just ask Tiger how that’s going. This student was hitting down as much as 7 degrees, causing all kinds of problems with ball flight control. But there’s more. You can lose as much as 5 yards of carry for every degree you hit down on the ball. So unless your club speed is really high, hitting down is a very bad idea, indeed. I rolled up a towel and placed it about one foot ahead of the ball and said, “okay, don’t hit the towel!” Well, as you might expect, the towel went flying the first couple of shots. Then I added a bit of instruction, “raise your belt buckle as far away from the ground as possible and stretch your left shoulder as far away from the ball as possible, and do so well before impact.” 
This photo shows fantastic execution of both moves, and as a result, his AoA improved dramatically to .6 upward. His ball flight also straightened out considerably. He is on his way to becoming a great driver of the ball. And, as a very, very good iron player, Look Out when he gets that driver working! The Towel Drill (plus the simple instructions concerning how to miss the towel) is a very effective way to improve your driving distance and accuracy. If you’d like to hit it farther and straighter, get to it!
Hit ‘em Great!