How to bunny hop on a mountain bike.
Step 1: put your seat a little lower than usual
Step 2: learn how to "manual" or get up on your back wheel
Step 3: shift your weight forwards while at the peak of your manual
After you learn the basics, you can try jumping up curbs at an angle. Why at an angle? Because you'll fuck your back wheel up if you don't make it all the way on to the curb. By going at an angle, you can safely learn this technique.
Once you get really comfortable with hopping, you can hop up anything you can get your front wheel on to. Just get up some speed, pull up hard, and shift your weight forwards to bring up your back wheel.
It's important to keep in mind that clipped pedals have nothing to do with bunnyhopping, in fact I recommend you learn without them. Hopping is strictly done with your body weight and handlebars.
Do not pull your whole bike up vertically. This technique (if you want to call it that) is very limited in how high it can get you, and it uses an insane amount of energy. Plus, it looks so ugly. Learning this way will only commit the wrongness into your muscle memory, and hinder your bunnyhopping skills for life. Don't do that, just learn the right way.
There are tons of great bunnyhop videos on YouTube that you can learn from, in fact the more of them your watch the more insight you'll get into different techniques. If you feel overwhelmed, just choose one video and stick to that advice, as information overload may work against you. I hope you learn to hop from my video! If you do, please post a video reply and show us what you've got!
DNM Dropper Post
I'm using a "dropper post" which makes it easy to adjust your seat while you're riding the bike. I like this since riding fast is easier with your seat up, and riding aggressive is easy with your seat done. Here's my review of the post: https://youtu.be/K35LXiExBh8 and here's where you can get one: http://amzn.to/1ChuVL8