The year of the bike and the size of the engine, how you have your sprockets geared all make a big difference. A liter bike will pop up at the flick of the wrist. Older 600cc bike need the clutch pulled in, throttle twisted just right (so you don't flip) and then dropped.
Everyone says it and its annoying at first, but it is true...it really does take time to get the feel for it.
If you pay attention to the stunt bike vids on you tube you'll see the guys run on deflated tires cause it helps with balance especially at slower speeds. But doing that isn't realistic or good for your tires if you ride on the streets regularly.
And I'm not talking about riding out one mile long wheelies here either. Im referring to just popping a wheelie or just short distance ones. Thats how you gotta start.