A good grip is the first requirement of a good golf swing, since your hands are your only contact with the club.
The Left Hand
The grip in the left hand should be where the last three fingers capture the club under the heel pad portion of the palm.
Variations of the Left Hand:
[Both are acceptable]
The left hand is rotated on the handle so one or two large knuckles become visible.
The left hand is rotated on the handle so three or four large knuckles become visible.