practice manualing first. then you'll be able to get your front tire up as high as you want, it's easy from there.. just pull up to whatever height, and lean forward, centering your weight, then pull the back of the bike up underneath you using your feet, and you can twist your handlbars too if it helps. in the air either try to get the back end back down first, or land even. then you're all set to ollie over a massive railing and astound anybody watching! goodluck!
the easitiest way to bunny hop is to just pull your front end up and than KEEP YOUR ARMS STRAIGHT don not bend them and lean forward it will feel like your feet come off the pedals and than just land even
once you get the technique down... try bunny hopping over stuff that will help you get higher... at least it did for me... I would just push myself to jump over whatever I threw out on the street