If you have cable, there's a couple of shows on the Outdoor Life Network that feature basic MTB skills.

Bunny-Hops are all about momentum and weight transfer. Pick a little object to jump over, something that won't spill you. You need a bit of speed, enough to carry you over the obstacle. As you approach, stand, then "compress" by squatting down suddenly. If you have suspension, you can feel it compress. Right before the object, spring back up strongly, like you're jumping. Try to twist the bars, like the guy above says. You do not need clips to do this, properly done the bike will "follow" you up.

Timing is everything. Squat, compress, spring up....one smooth sequence.