There are a few requirements for the golf grip in the perfect golf swing.
First and foremost, the grip should be taken in such a way that allows the golfer to most easily square the club face at impact with minimal to no manipulation. After all, what good is a great golf swing that slices the ball into the woods?
Second, the golf grip should be taken in such a way that the golfer can apply leverage to help maintain lag. Many golfers that I see in daily golf lessons tend to have a very weak left hand grip on the golf club. This places the pad of the left hand to the side of the club shaft rather than on top of it, making it impossible to use the bones of the forearm and wrist joint for leverage. Here is a great golf instruction video and article on how the golf grip will effect your golf swing lag.
Third, the grip should allow the golfer to hold the club securely without requiring a great deal of muscular tension. Setting the hands up correctly on the club with minimal tension will allow the golfer to have the wrists relaxed during the golf swing which is critical for increasing the lag during the downswing and allowing the club to release naturally and freely with great speed.
So, those are the three requirements for the perfect golf grip, what does it look like?
This image is taken from the RotarySwing Tour golf instruction book written by Chuck Quinton. The book goes into painstaking detail about to take the proper golf grip.
What you want to observe here is the red line that is drawn from the space between the right thumb and forefinger. Or, more simply put, it runs parallel to the right thumb. This is where most golfers go very wrong with the golf grip. They tend to have a very weak grip where this line is pointing more at their face rather than toward the right shoulder. This makes it much more difficult to square the club face at impact as the right hand has to aggressively rotate through the hitting area. Obviously, this doesn't meet requirement number 1 of the perfect grip.
However, having the right hand positioned as pictured above makes it much easier to square the clubface at impact. Now, let's take a look at the left hand.
Like the right hand, the red line points toward the right shoulder, only not quite as far. That is because the two lines formed by both hands should run parallel to each other when gripping the golf club. This meets requirements numbers 2 and 3.
Having the left hand in this position that would be considered slightly stronger than neutral allows the left hand to apply leverage to the butt of the golf club while also allowing the golfer to hold the club lightly.
Meeting these three requirements for the golf grip make it much easier to start building your perfect golf swing step by step. Starting out with a poor grip will make it necessary to build compensations into your golf swing that will cause you more problems down the road, so it's best to start out with it right from the beginning. If you need to rework your grip, watch these videos that go more in depth on how to grip the golf club.