Golf is a cruel game. Sometimes the swing you want produces the very ball flight you were trying to avoid. Such is the case with a hook. If you're afraid of hitting the ball left of your target, your tendency is to slow your body turn. You think if your upper torso turns left of the target, the ball will follow.
Ironically, the opposite is true. By slowing or even stopping your turn toward the target (inset), your arms and hands whip through the hitting area and shut the clubface, producing that dreaded snap hook.
To prevent the clubface from getting shut at impact, you've got to keep turning. It's hard to convince yourself to do this, but you have to trust it. Let your chest and hips rotate forward until your shirt buttons and belt buckle point left of your target (large photo).
This stops the clubface from flipping closed and will help keep your ball in play.