Like 99bird has stated, the key to any good paint job is preparation....clean is the name of the game. Removing rust, debris, old loose paint and any chemicals (including the oils from your hands) is required to get a lasting finish.
Another component is choice of paints...for frame work, if you don't want to go the powdercoat route, your next best choice would be an epoxy finish. These paints are a little harder to apply than laquers, but give a surface almost as durable as powdercoat. They require mixing just prior to application with a sprayer, and require a special nozzle because they are more viscous, but the results are worth it. Once epoxy finishes have set up, little other than a nuclear blast is going to put a dent in them.
The next best choice are catalyzed high temp laquers; they also require mixing just prior to application, and the finish needs to be heated (in an oven for small stuff; a heat booth can be made with a couple heatlamps for frames) to get the best durabilty. Rattle can high temps would then be the next best choice, and then traitional laquers down at the bottom of the scale.
Careful prep is the key to any lasting paint job.