The most frequent complaint that I get as a teaching professional is that the student slices the ball, therefore, losing distance and accuracy. The problem with a slice is that is has two main possible causes, or a combination of the two. This can sometimes make it difficult to diagnose the problem, and therefore difficult to fix.
Cause #1 - Open club face at impact.
Cause #2 - Swing path too much outside in.
Many people will simply change their grip to try to fix a slice, but if the problem is swing path, changing the grip will actually make things worse.
Check for swing path first...the golf club should approach the ball slightly from the inside of the ball. This will cause the ball to take off slightly to the right of the target. Look at your divots...if the divot is angled way to the left, your path is too much from the outside. A good drill for bad path is to place a cardboard box about an inch beyond the ball. Try to hit the ball without hitting the box. This will insure an inside to inside swing path.
If the ball is still slicing, the club face is open to the path. Have a professional check your grip. Then learn to shut the toe of the club over the heel of the club through impact. Think about trying to stab the ball with the very toe of the club. Use this thought until the ball is consistantly hooking to the left, then quiet your hands more and more until the ball is flying straight.
From our Golf Pro, Fred Christian, Deer Run Golf Club