rock forward then rock back so you are up on the back wheel, you will get to a point where you feel the front wheel is not going to fall back to the ground, when you reach this point push down on the bike (make sure your tyre is not rock solid) keeping the rear break on, and stand back up on the pedals (in a fast motion) from that crouched down position lifting the bars as you do so, this is how i learnt, not sure if it will help at all:)