Hooking was my nemisis untill the other day, I could do sloped walls fairly easily, but virtical ones seemed impossible.
There is an upside down canal boat on the towpath near my house, its about shoulder hight. Its as virtical as your gonna get and I have always wanted to try it, but was too scared.
The other say I just thought sod it! I tryed it and it was easier than I thought.
I can get to bash nearly every time, but a few times I got it to rear wheel only to have my brake slip (dam disk!) one time it didnt slip but my weight was too far back I just pivoted on my back wheel over the edge.
This has put a whole new light on hooks for me, I want to try some different ones, but there arnt any more around me (Y)
TIPs
fast, be confident, weight forward, be confident.