Basically, it's: boost - jump - land -boost - jump - land over and over again while moving (I precise the "land" part because the boosting must be done on the ground). To be really efficient, you need to shorten as much as possible the boost period and you need to boost again the very moment you hit the ground (Normally, once you've mastered the "technique" , you should never land and boost on the ground (unless it's on purpose) and already be jumping again). First, try it in an empty room, where you're not disturbed by anything, then learn to do it against an opponent. The basis are quite quick to learn, but you'll still need skills to make good use of this "technique".
It's hard to show you a video tutorial of "How to bunny hop", since no one made one. Instead, I give you a video of a fight against Zinaida. I know it's a bad example, since the player has to move his lock-box up and down to keep track of her, so you don't really see what the AC is doing. You can look at others of his videos, you might learn some things. This guy is pretty skilled, don't expect to reach his level just by watching his video.
Another way to learn: just watch what the opponent in the arena are doing (when not flying around). Most of the "decent" opponents use bunny hop, so just try to mimic them.
Bunny hopping is not that hard to get used to, and you should have learned to use that already through practice by the time your skill reaches mid-level. Bunny hopping is also basically like quick boosting in ACFA, except that you don't look as stupid.
Are you a scrub? http://www.sirlin.net/ptw-book/intermediates-guide.html