O.k. well bunnyhopping is probably one of the most frequently asked how to's, and i usually dont respond to them because it's an easy concept, but kinda hard to explain exactly how to learn them and it always different for every person. but ill try and explain it as best I can.....
begin by riding at a medium pace, bend down a little so you are kind of hunched over the bars a little and your arms are bent. Now bring your body up fast, but dont pull up on the bike, just let your arms straighten out. As soon as your arms are straight, now pull them and the bars up close to your chest, with the momentum of your body and you pulling your arms up, you should be able to get the front of the bike up pretty high. And once you learn to get the rear up and combine everything youll be able to get it up even higher.
Now the back of the bike.... As soon as you get the bars up near your chest and the front of the bike is close to as high as its gonna go, push your arms back out, but instead of putting them straight back down, push them out in front of you, at the same time, pull you legs up, doing all this at the right time will (hopefully) get the rear end of the bike up. REMEMBER!! All of this must be done in a relatively short period of time.
Ok this isnt technically a "Bunnyhop" yet because you didnt bring both tires up at the same time, but you need to learn this before you try getting them both up at the same time. Its basically the same concept, but in and even shorter period of time.
TRY THIS!! - If your still having triouble, try bunnyhopping OVER
something I.E. - A backpack, a cup, ect... Ive found that I have more trouble just bunnyhoping off flat ground than if I try gettig over something. I can usually get a lot higher.
I hope this helped and if you have any more questions, just ask