The problem: Failing to shift your weight back to your front side on the downswing (a.k.a. "hanging back"), which often yields fat shots and slices.
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Simple fix: Golf impact bags ($40) help you learn to shift your weight correctly, "but a spare tire works just as well," says Goldstein. "Hit it with a midiron, at about 75 percent, holding at impact. Your right knee and foot should shift into your left side, and your hands should be slightly ahead of the clubhead. Do this 10 times to ingrain that feel, then hit a golf ball."