To fix a slice, have a friend hold two shafts, one above the other, against your club at address. Then try to hit the lower shaft on your downswing.
I've learned a great many lessons from different sources, including students, top players and fellow instructors.
One such colleague is Peter Kostis, who years ago taught with me in the Golf Digest Schools. I saw Peter give this drill to golfers whose lower body and hands got ahead of the ball on the downswing -- a problem common to many golfers, particularly those struggling to square the clubface.
As these students addressed the ball, Peter held two shafts in line with their clubshaft, as I'm doing above. He told them to feel as if their club's shaft would contact the lower shaft before the upper shaft as they swung through. (He pulled the shafts away just before impact.)
Do this drill with your teacher or a friend. It encourages you to release the clubhead earlier in the downswing, which squares the clubface at impact and straightens the ball flight. Release your arms; don't flip your wrists. You've overcooked it when you start hitting hooks and fat shots.
Ranked No. 5 by his peers among Golf Digest's 50 Greatest Teachers, Flick is based at the TaylorMade Performance and Research Lab in Carlsbad, Calif. View more tips from Jim Flick.