Ditto all the prep work makes the difference. Sand it clean, the finer sanding you do first, the less later. Use a good auto body primer, and fine sand that down too. Block sanding is tough on a bike because there's almost no flat surfaces, so its all hand work. I'll jump in on the Dupli-Color crew too, available at Autozone or O'Reilly's or other autoparts stores. That paint just flows on, I also warm the cans up in the sink with some hot water, shake, hot water, shake, hot water, shake... I think that would help any paint...
Now that all said, IF I had a nice high dollar bike I was redoing, I'd save up for a professional paint job. No powdercoat for me cause IF I'm ponying up some cash I want a nice candy coat or something else more exotic...
Carl.