This is a great tutorial that covers the Rear Naked Choke. It is pretty in depth and covers many fine details about how to finish the Rear Naked Choke. The video was inspired by many greats including Marcelo Garcia.
They start by covering the Over / Under Control. Of the two that he goes over I feel that the first grip, the Ball & Socket, allows you to stick to your opponent's back better than using the Gable Grip.
The only thing that I would do differently with the Ball & Socket grip is grab my fist of the Overhook instead of my wrist as demonstrated in the video. Once you have your hands locked and you squeeze your fist into his chest the grip will be a lot tighter than if you grab your wrist. That is a little tip I got from Babs who was one of Marcelo Garcia's training partners.
