It takes a lot of practice for sure...I find it's easier to learn with a brake that's on smooth rims without tar, but still has hold. Also, try pedaling if your front wheel starts to fall. This might help you for a while to get the hang of it, but don't rely on it. I learned to manual on my DJ bike. I used to pull sitting down wheelies, then reach a certain speed, and just coast without pedaling (while sitting down of course), I found I could go for well over 100 feet just coasting like that, and then when I got my trials bike (seatless, lol) I had something to go on. It's really all about finding that balance point, and knowing how to make SMALL leg pumping adjustments, and feathering the brake.