One great thing about this Fork Glide tutorial from Coloradoflats' VFI series is that it focuses solely on teaching you the actual rolling Fork Glide position. Too many other online tutorials that we've seen will try to throw you in too deep too soon, lumping the straight rolling component of the trick in with 1) the 180-degree pivot from a normal bicycle riding position into the Fork Glide position (called a Half Hydrant); and 2) the rideout (transition from the trick position back into a normal bicycle riding position).
Make it easy on yourself by mastering the rolling-in-a-straight-line portion first! The Half Hydrant and the rideout are separate techniques that each warrant individual consideration of their own at a later point. It's hard enough to learn one technique at a time, let alone three. So start by just learning to roll in the Fork Glide position, and move on from there after you've mastered it.
Next up are some more pointers on learning the Fork Glide, including the necessity of offsetting your own body weight, and not letting the bars turn in a way that can cause you to slam.
So what does it look like when someone who has never tried flatland tricks before gets on a bike and tries to learn the fork glide? To find out, we took a complete newbie (he doesn't even own a BMX bike), taught him how to fork glide, and documented the whole thing on video. Click the link at the end of this sentence to check out the adventures of our friend Dan as he attempts to learn his first flatland trick.