A lot of the players that I work with seem to have a problem with their grip.
For most of them, the problem is with their top hand -- for a right-handed player that's the left hand.
Besides balance, learning to place your top hand on the club correctly is the most important thing about making a good golf swing. A poor grip often leads to a slice.
Fortunately, there's an easy way to find out if you have the correct grip.
For a right-handed player to make the proper golf grip, the left hand has to be rotated to the right with the thumb curved back. When you're in your stance, if your grip is correct, you should be able to see the knuckles of your index and middle finger.
Most players I see don't rotate their hand enough; they can't see their knuckles. This causes them to slice the ball.
To see if your hand is in the right place, take a Sharpie and make two marks on your glove at the knuckles. You should be able to see two marks when you stand over the ball.
This is a very simple solution to one of the most common problems I see.
Turn your left hand to the right for a stronger grip. This will allow the toe of the club to rotate past the heel and help you eliminate your slice.