The slice is always a big issue for many golfers . Master key to solve it fast can be the rotation of your right and left hand on the golf grip.
The neutral position of your hands (for most golfers with good range of motion in their body) on the grip is this:
When you grip the club with your left hand (RH player). The club grip will cross the palm of your hand (see picture). Try to hide the "x" when you place the grip in your left hand.
Place grip across the palm and try to hide the "x"
When the left hand is placed correctly on the grip. You will see the index and middlefinger knuckles at address.
At complete address you should see these knuckles marked with the "x". Caution! Important that you see them without moving your head from your "starting" position of the swing.