A two-footed take off is easier for learning, but you can do it with one. Eyes on the rail making sure you grab it, and bent knees to drive in the next step.

This is the most important part of the move. You have to begin your rotation from the moment you take off the ground, so you're already twisting when you take off. Head is going left (following the rule that your body follows your head). Body is quite tight for a semi-tuck to speed up rotation.

Leaning into the rail allows the momentum from your run-up to keep you going over it. Bringing the legs up will assist in gaining height, and speeding up the rotation.

You can do this with your loose arm spread out for style, it doesn't really matter.

This shot clearly shows how tucked you are when doing this move, like all rotations, the shape of your body dictates the speed that you rotate. The head is still rotating towards the rotation, bringing the rest of the body with it.

Once you've felt you're over the rail (subconsciously you'll know), kicking out the legs slows the rotation so that you can control the landing.

One footed landing allows for a quick run away.

The end!

If you're grabbing the rail with your right hand, just focus on getting your hand on the rail, bending down slightly and thrusting downwards with your legs whilst your torso begins rotating anti-clockwise. Whilst you're travelling vertically, begin tucking to aid that twisting motion, and landing is pretty self-explanatory.