Set the toe in a closed position, then take your grip.
Golfers who hit a weak slice have two basic problems: They cut across the ball with an out-to-in swing path, and they have an open clubface at impact. Knowing this, you can eliminate one of these problems--the open face--from the start, simply by turning the clubface closed before you take your grip.
To set the clubface in the same closed position every time, hold the club in front of your chest and visualize an imaginary clockface. Rotate the toe from 12 o'clock (square) to 11 o'clock (closed) from your perspective. Do not grip the club and then turn the toe to 11 o'clock, as you're just rotating your hands and not closing the face.
Setting the clubface in a closed position before gripping the club ensures a closed face throughout the swing, producing more solid contact and a ball flight that goes left. Also, once your shots start consistently curving to the left, you'll adjust to your new ball flight and stop swinging from out to in. You'll figure out that you have to make a downswing from inside the target line to get the ball starting right and drawing to your target.
Once you've honed the proper swing path, you can return the clubface to the 12 o'clock position before taking your grip. If your slice ever comes back, you'll know how to fix it.
Based at ChampionsGate near Orlando, David Leadbetter operates 28 golf academies worldwide.