Advice from a novice.
As much as I do not like it.....
Lay on your back, bridge up. Spin, now that you are facing the mat, spin, now that you are faceing the ceiling, spin......I think you get the idea.
The spin is more of a stepping over i suppose.
Personally, I have a hard time with this one due to my size.
However, Sensei Sanner, who usually leads this drill, has a neck like a bull and can bridge with the bulk of my weight upon him (280+ lbs)
He also is extremely difficult to choke. i am not sure if this is a direct benefit of the bridgeing, but I suspect it helps.
The good days are like the bad days.....only better.