Proper balance is the foundation of every efficient swing, and the Key to good balance is having an anatomically correct address position. In other words, your body should be perfectly positioned before you swing. Here's my favorite drill to learn the correct address posture. (You can do it anywhere, because you don't need a ball.)
1. Take a driver and stand straight up with your feet shoulder-width apart. Look directly ahead—keep your chin up!—while holding the driver gently against your chest. The butt end of the club should touch the bottom of your chin, and the clubhead should hang straight down (A).
2. Slowly bend forward at the pelvis, keeping your neck straight and the driver parallel to your chest until the clubhead sits directly between your knees (B) or a shade behind them. You want to bend forward about 30 degrees.
3. Shift your left hip slightly toward the target until the clubhead touches the target-side knee (in my case, the left) or the inside of your calf muscle. Be sure not to make the common error of turning your hips.
4. Add a little flex in the knees, let your arms hang down and grip the club (C). Now you're perfectly balanced and ready to swing away.