How you transition from backswing to downswing largely determines the success you'll have at impact. If you're a slicer, your typical move at this point in the swing is to cast the club outward with your hands. The most straightforward fix, of course, is to keep the clubhead inside your target line as you near impact, but this idea can come with its own set of issues if you take it to the extreme.
STUCK IN THE MIDDLE
The danger in overemphasizing an inside-to-out swing in an effort to avoid casting is that you'll eventually begin tucking your right elbow deep into your right hip. This super-narrow downswing brings the shaft way too close to your body; even if you manage to square the clubface from here, you'll block the ball out right. (If you manage to close the face, the ball will hook wildly to the left.) It's a double-miss that'll drive your scores deep into the black.
WIDEN TO IMPACT
Here's the fix: As you start down, think "wide left arm." This doesn't mean releasing your wrists early — that's casting. Instead, keep your right shoulder nice and high and gradually release your right arm, allowing your wrists to unhinge on their own. It's not only a slice fix, it's a power move — you can pick up as much as 10 mph by "going wide." Not only will the ball fly straighter, it'll soar a lot farther.