If you're busy or don't live at a convenient distance from a driving range, practice your backswing at home with a new twist: make your backswing last an entire minute. This technique has been proven to match the effectiveness of hitting thousands of balls.
When you reduce your backswing to extra-slow-motion speed, your concentration and muscle memory soar to new levels. Get into your address posture with your driver, and then start the clubback very slowly. The club should literally move at a snail's pace. Follow the pace indicated by the photo (i.e., take 10 seconds to swing your hands from address to mid-thigh, then another 10 seconds to get the shaft almost to parallel, and so on). Don't just swing to the positions and stop the motion should be extra slow, but you should never stop moving. Keep in mind that this is more of a workout than you might think (you'll see what I mean as soon as you get to the top).
Perform this drill every morning before work, and after a week take your new backswing to the range. You'll be surprised at your results, and how easily your body remembers the positions you practiced in your slow-motion swing.
Note: This technique works for your downswing and through-swing, too. After a few weeks of practicing these swing sections over the span of a minute, try making your full swing over 3 and then 5 minutes.