In this video I go over some of the basic controlling concepts of back control and then cover the way that I do the Rear Naked Choke (RNC).
When controlling the back I like to keep a pocket (in the seated position). This leaves my hips mobile and gives some resistance against my opponent flattening me out (which is a common defense from the back).
I opt to control double under grips to start off. This is not necessarily a better control than the seatbelt grip but I believe that for many beginners this gives a little bit of stability to the position so that they can set up their submissions without losing the position.
With the double under grip it will be very difficult for your opponent to reverse shrimp, turn his/her back to the floor or roll to his/her knees. It is also a great setup for the future chokes where turning the lapel out can help set that anchor hand.
After controlling the lapels I choose to place my head against my opponents back. This will make it difficult for him/her to take up that space that you have created in the pocket. Often if the person has not grappled with you before they will probably not even expect the space in the pocket and if you push the head into the back it feels almost exactly like a normal back control. There is only one thing better than pulling someone into the pocket for an armbar or a choke...pulling an unsuspecting opponent into the pocket for a choke or armbar.
Once you have mastered the pocket and the spacing of your hips then it's time to bust out that ole faithful submission the RNC. The pocket insures that no opponent will be to tall to receive this submission. Often when doing this submission against someone that is your size it can be difficult because you are reaching up and over their shoulder/collarbone area and then trying to come back around the neck. It often leaves me wishing I had go go gaget arms.
Reference the video to see how I finish my RNC choke and dont make the same mistakes that I made as a white belt and a blue belt. Never reach in front of your opponent to clasp your hand to the biceps and make sure to compress your opponent not stretch them.