Mostly just practicing. There are some links to some trials skills, but I can't remember the link. If you do a search for "Bunny Hopping" you should turn up the link.
It's really just a matter of spending time on your bike. I've been practicing riding "skinnies" for about 6 months by riding curbs w/o sidewalks around my neighborhood. In the beginning, I was happy to ride 10'. Now, I can ride as far as I want and was actually riding some wheelies on the curb.
L8R
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"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger