When I learned this, I found a dirt path in a local city park with a lot of tree roots- some pretty hefty. This gave me a training ground, an obstacle course to drill on several times a week. (this is how young horses are taught to jump for cross country too) Roots are good because they're small enough to botch the jump and the fork will save you from a faceplant. They're big enough and varied enough for a real trail experience. Launching out off the mud is how you may as well start- That's what you'll do on the trail. Parks are usually pretty tame, a bunny slope compared to a good trail. This is where you want to screw up and fall while you learn.
Loading the fork is a good way to start just getting the front end off the ground, but it's ultimately a balance shift combined with the leg hop that does it. You have to learn this with your body more than your mind, too, so be prepared to put time into bad jumps over half inch roots. I learned to hop at 42, and then spent two years at a big university scooting around on a BMX cruiser jumping stuff and riding stairs. The freak out factor for snotty little boys was worth every fall I took in Audubon Park. (heh heh!) Just make sure your fork is serviced- stiction or bad oil will make it tougher to control a hop and wipe out the safety factor the fork supplies.
Go kick its ***, girl

Miss Liz