I can tell you how I do it. My hand that is on the floor, I push it into the floor to get my spine up as straight as possible within my comfortable capacity. Then I push my knee and upper arm against each other which rotates my spine. I rotate my head and the shoulder of the arm that is pushing into the floor in the same direction to help increase the rotation as well. So there are two basic vectors or directions of movement occuring. One straightening the spine up and the other rotating around this.