If your already able to put your leg behind your head comfortably and want to try it standing with this subroutine it's probably a good idea to make sure your sufficiently warmed up and stretched out. The Utkatasana is a good place to start for the work on the hips, uttanasana for the forward bend and I highly recommend the Uthita padangusthasana and especially the standing marchi subroutines. The standing marchi will do a good job of pushing your hip back.
For leg behind head postures in general I made a video recently on approaching the posture in Vinyasa Karma. In the video I approach the standing LBH from seated, putting the leg behind my head and then moving into the LBH forward bend Skandasana or Richikasana. Here's the link
To get the leg behind the head in standing you want to bend forward, take the leg over above your elbow, push the hip back ( why standing marchi is useful prep) and take the foot over and around your head dipping your head in at the same time.
Shuffle the foot a little further behind with your shoulder, you want to have your leg far enough around that the foot isn't pushing too strongly on your neck.
Next it's case of straightening up although your always likely to be a little stooped...unless your nine. one way is to walk the hands up the leg but that's a bit of a cheat, better is to stretch out of your hips just as we've been doing in the On your feet sequences and keeping your back strong.
It's advisable perhaps. to have done some work on back bending postures to make your back stronger before moving on to leg behind head postures.
One more thing that I remembered practicing this earlier, I think we tend to be afraid of falling out of this and landing awkwardly and painfully with our leg still behind our head. I've stumbled in this a couple of times, this evening included and always the leg pops back from behind the leg neatly giving you time to stop yourself falling. It's tricky, can take a couple of attempts if you haven't practiced it for a while or if it's your first time.
NB: These are practice notes that will be tidied up and put into the new edition of my Vinyasa Yoga Practice Book along with the current sequences and subroutines. The book can be freely downloadedHERE. There is a page on Facebook HERE with all the latest sheets and updates. This book is in no way a substitute for Ramaswami's Complete Book of Vinyasa Yoga.