Building up inertia
1° Start with enough room for about 2 pedal turns and launch a fast pedal hop.
2° Land the rear wheel about a bike's length from the obstacle, and lower the front.
3° Follow up by another pedal kick, with full extension and using the bouncing effect.
4° Once in the air, shoulders above the bars, aim the front wheel at the edge while pulling the bike with you.
5° When the front wheel gets in contact with the edge, brakes full on, the momentum will tilt the bike forward, keep your body moving forward.
6° After you've just folded completely, move away past the edge by releasing progressively the front brake, and extending the arms.
Roll forward and finish off the move until the rear wheel is secure above the edge, or do a quick front-to-back wheel swap if there is no room for the full bike. (Woody is left foot forward, that'd be the other way round if you are right footed). See this move in a video and in this slow-motion video
Bounce from the first pedal hop
pick the front wheel on top
Getting the move right:
Really, you should start on small walls, maximum about the height of a wheel, to gain confidence. It helps to approach the obstacle with a 45° angle, like when learning the "wrong side" pedal hop landing on the front, before you try the frontal approach. This move can lead to nasty face-plants against typically blunt, rather indifferent concrete edges. So good brakes are a must. Maybe a good starter is to do a basic pedal hop, followed straight away with a basic endo onto a smallish kerb. From there, try to release the endo and control the weight shifting forward. Once you get this, launch the pedal hop faster, to land clearly on the front wheel, with enough momentum to lift the rear wheel above the horizontal. Indeed, the faster you go, the easier it is to lean over the front-wheel.
Transfer your weight over the bars
Front-to-back wheel swap
Then you can add the second pedal hop impulse to boost things further in your favor. Again, some guys will land this move on just anything, including rails or fences, and carry on with a front-to-back wheel transfer. You really need to throw your shoulders beyond the edge where the front wheel is stuck, so that you can land and stay in balance on the front wheel. Only then, you can release the brakes and roll further, or turn on the front wheel to position the rear tyre on a nearby edge.