A very common fault with the grip is to place the handle too much into the palm of the hands.

Assume throwing a baseball. It is natural to place the ball into the fingers of the hand vs. the palm. This enables the player to toss the ball with force and control. Likewise in the golf swing this should also take place and can only br donr in the fingers of the grip.

Take two yardsticks and fasten them flat together. Lay the yardstick across your target hand (left hand for right handed golfers) with the bottom edges running along the calluses at the base of your fingers. Specifically the stick will fall into the second digits of the target hand. 

Now fit your rear hand (right hand for right handed golfers) to your target hand noticing also how the yardstick naturally provides a ridge that is automatically caught into the fingers of the back hand. Practice this grip while hinging the yardstick at the wrists up and down. One of the benefits of placing the grip in the fingers is the wrists can hinge freely, thus allowing for more leverage and club head speed throughout a golf swing.