The next time you watch pros hit the driver, pay attention to how smoothly they make the transition from backswing to downswing. Many amateurs rush this change of direction, which results in a loss of distance and direction.
Living close to the Orlando-area theme parks all these years, I've come to think that your transition should imitate the movement of a roller-coaster car at the top of the track. As it goes up and over a peak and then starts down, its speed is roughly the same. The acceleration on the downslope is gradual and culminates at the bottom of the track. Your swing should resemble this.
Focus on the rhythm of your transition, making the first part of the downswing as smooth as the last part of the backswing. The club should then pick up speed as it moves through impact. The best way to get a feel for this gradual acceleration is to start the move forward with your lower body, and let your hands and arms follow.
David Leadbetter is a Golf Digest Teaching Professional based at ChampionsGate, near Orlando. He operates 26 golf academies worldwide.