Well, you need to say which way you bunnyhop: do you pick up both tires at the same time, or do you pick up your front tire first, then your back?
If you bunnyhop by picking up both tires at the same time, you might as well stop. This way is almost useless, and you will probably not go anywhere with it. Do yourself a big favor and learn the other way.
Now, if you pick up your front tire and then your back, you just need to practice. To get higher in the air you need to lean back more, then lean forward more once the back tire leaves the ground. But to really figure this out you just need to do it more. Good way to practice is to find small cardboard boxes to bunnyhop over. After a while it all starts falling into place.