One of the most important factors in playing good, consistent golf is the grip. Barely seeing any knuckles on the left hand results in a weak grip and a slice.
Too many knuckles, however, will see you with too strong a grip, which results in pulling or hooking the ball. The first thing a golf school instructor will tell you about the grip is always to show two knuckles on your left hand.
Get your grip right and you're halfway there.