Right.. Here is my tip.. Start off small. I.E. A kirb for example and manual the bike up onto the back wheel, lock the front brake and then kick the bike so you get momentum going then instead of landing on the back wheel push your weight to the front of the bike for it to land on the front and then swing the bike round to land your back wheel on the kirb. Give that a try and gradually work yourself higher and higher untill you are getting a decent height