HOW TO GET IT: Grip your driver with just your left hand and take the club back like you're making a regular full swing. Make sure you turn your torso slightly away from the target and hinge your wrist fully. Stop when your hand reaches belt height and check that the toe of your driver is pointing up. If you've done it right, your left elbow should point down the target line.
Now, swing your club to impact position and stop. If you've simply swung your left arm down, you'll see that your left elbow still points down the target line and the face is open. The trick is to swing your arm down while also rotating it so that at impact your left elbow points slightly behind you. Check the face it'll be square.
When you're waiting to hit on the tee box, make waist-high-to-waist-high swings. On each effort, get the toe of your driver pointing up in your backswing and in your follow-through. That's the rotation action you need to square the face at impact.
...but points behind you at impact.