Find the local auto parts outlet that sells real paint to the autobody shops in your area. They will sell you good primer for steel and for aluminum. Modern primers will grab onto a clean, scuffed up surface without any problems.

The top coats depend on what your spray gear is. If you have a place where can spray polyurethan safely, you can buy an entry level HVLP set up and produce great results. OR perhaps your local EAA chapter has the gear and you can use it.

There is no magic, just takes practice. Never thought that I would own 8000 grit sand paper. My wonderful wife says that my fuel tank is the best looking one that no one will ever see. And a fuel tanks is a great part to start learning to spray on for that very reason.

Remember to use breathing protection. Polyurethane paint will kill you in short order if you breath the overspray.

EAA publishes lots of good info on how to do this. And my local auto paint supplier is happy to explain stuff.

Aircraft painting in 2012 is no different than painting a truck or car. The technology has converged.

Best of luck,

Wes