There's a surefire way to prevent a topped shot: Shift your weight to your front foot before impact. This will keep you from falling away from the target or back onto your heels, the two main causes of topping the ball.

To groove a good weight shift, practice hitting 5-irons with the ball teed up a half inch. Try to take a divot after impact without hitting the tee. With a sharply descending blow, you'll get your weight onto your front foot and make contact below the ball's equator.