Do it on every super low, easy box you can find, and try them both ways. Try not to look down, as that can put you off axis. Commit to the spin, and just trust that you will get all the way around. When you come around, try and spot the end of the rail over your shoulder. it will help you lock onto it better.
The worst thing you can do is switch rack a tall hand rail. Your nuts will catch hard, and then you backslap on that bitch.