Most amateurs hit the ball with a downward strike too low on the face, creating high spin and low launch—the worst combination for distance. You'll immediately get longer if you hit it in the sweet spot, which is a little above the center of the face.
To do that, focus on how your driver approaches the ball. By the time your hands swing down next to your legs (above), it should feel like the driver is about to brush the grass behind the ball. This gets the club moving upward before impact—an instant power booster.
You need a good downswing sequence to transfer energy from your body and arms into the clubhead, but a big, out-of-control backswing (below) ruins the ability to do that—so your backswing matters. Turn with your shoulders only as far as you can go without straining.
You should feel pressure in the instep of your back foot, but not on the outside of it. Meanwhile, your foot closest to the target will feel light on the ground. From here, a good downswing starts by pushing hard into the ground with that front foot, like stepping on the accelerator pedal of a dragster.
One of the misconceptions about power is that you get it by keeping your wrists hinged so the clubhead lags behind your hands through impact (below). That's no way to generate speed.
It also makes it really hard to deliver the face square and with enough loft for that high launch. Instead, let your wrists unhinge and freewheel the clubhead through impact.
It should be passing your hands as it strikes the ball. Try this drill: Mimic a backswing with your right arm only. Swing down from the top pretending like you were going to slap the ball into the fairway with the palm of that hand.
You wouldn't hit the ball with the heel of your palm. You would let your wrist unhinge abruptly, giving the ball a good smack. Put that feeling of wrist release into your downswing when you hit drives, and 10 more yards—or more—will suddenly appear. — with Matthew Rudy