Well I have to admit that I've been avoiding this exercise for a while now. The reason for this is my poor upper back mobility. So every time I've been trying it I have failed completly and basically crashed.
Today I started to do them against a wall (thanks for the tip Cole) and I could actually do e few reps. So this at least got me started
getting used to the movement and hopefully with time I can get away from the wall.
Hope this helps others getting started on this movement.