To make this even easier I use the illustration of gripping the ball
To make that work for the guitar though, you have to start with the ball resting at the place where the fingers meet the palm, not in the center of your palm (i.e. resting on the ring of the ring finger) :
Then curl your fingers around the ball:
Now the view without the ball
same pose facing you (note that you should extend your pink a little to line up with the fingers:
The next step is BIG - you need to bend at the wrist:
same view facing you:
just move your thumb to the middle for good grip at the back of the neck for classic grip:
I apologize if I have included too many pictures, but I think that this topic deserves a lot of discussion. I’ll be glad to hear from others if you think that I have some things wrong.