Doing a J-Hop is a bit more tricky than the bunny hop, if nothing else for the fact that it requires weight shift, not just leg spring. However, J-hopping is more applicable on the trail (and it's more impressive) because your front wheel enters the air before the back, which means that you can jump higher and that you can take flight a tad later, since you don't have to worry about your front wheel hitting the obstacle. Let's do this. Ready?

1. Find a flat area and start coasting while standing up. Make sure you have enough speed to be balanced comfortably, but not so much that you crash and burn upon failure. Once you get better, you can place an obstacle such as a log on the ground to hop over.
2. Rock your body weight forward a little to get some momentum, and then throw your weight backwards, pulling back on the handlebars. Imagine the small of your back leading the rest of you into the rear. Don't just throw your weight back, though; "jump" with your legs as well for some upward momentum. Practice to find a good combination of these two motions that will get your front wheel a good bit off the ground (no wheelies allowed!).
3. When your front wheel has reached it's "peak," just before it stops rising altogether, lift up the back wheel with the friction of your foot against the pedal, just like in a regular bunny hop. It's important that you make a "jumping" motion with your legs back in step two, because they need to be extended in this step to lift your back wheel towards your body!
4. Let the back wheel land first, your weight remaining in the rear. If your wieght is forward at this point, your front wheel with smash down not-so-smoothly; it's not a good feeling.

Part of what makes the J-hop so hard is that you need such a fluidity in weight transfer. To develop this, unfortunately, practice is required. Once you get good at J-hopping, here are some other tidbits to think about:

• Practice your timing so that you can lift the front wheel as you approach an obstacle, and take flight with your back wheel at the last moment. This makes it possible to clear objects at slower speeds.
• You can hop sideways onto surfaces parallel to your bike if you are weighted slightly in that direction as you lift the front wheel. Imagine beginning a turn, but then popping your wheel up instead.
• Using the simple front wheel pop without actually taking flight is infinitely useful as well. It's great when hitting a patch of mud or a puddle at speed.