"I have never met a good golfer with a bad grip." Arnold Palmer
The golf grip is the primary source of power and feel. Both aspects are important to a good golf swing and repeating shots. The golf grip is also the most difficult item to change.
"How do I know if I have a good golf grip?"
Everyone's golf grip should be unique to their body. Our hands and arms are not all the same.
The easy test. Grab a hammer with your dominate hand. Note the position that your hand is facing relative to the head of the hammer. If you can hit a nail on its head with a hammer than a large golf ball with a bigger club should be easier. Now grab your golf club with the same hand orientation. You will automatically grab the golf club in the most efficient position to generate power and control.
Taking your golf grip is an over learned skill perfected by repeated practice. Simply take your grip while watching the NFL playoffs and you will have a new grip by February.