There are a few keys to painting. Most of which have nothing to do with actual painting.
Data sheet: 45% of the battle! When you buy your paint, you get this piece of paper. It tells you what pressure, tip size, mix ratio, kick time and everything else about your paint and everything to do with the paint before and while you apply it. To quote a ticketed freind of mine "If the paper says lick your finger and stick it in your ass, do it!". Just do everything the data sheet says.
Prep! Another 45% of the battle. Clean, clean, clean and clean some more! There is no such thing as too clean for a good paint job! I did some aluminum honda civic rims for a guy last wheek while I posted my first post here. After sanding with 120 and removing all the crap, I used brown scotch brite and alcohol to scuff EVERYTHING else on the rim. Following that I cleaned all the left over gunk with a garden hose (constant running water) and more brown scotch brite to wash them off ans scuff some more. After that I went over them about three times with alcohol and a rag untill the rags came off the rims clean.
Painting, only 10% of the battle! Most of this comes down to the data sheet again. First coat of primer should be just a light dusting. All primer does is give the paint something better to hang on to. Second coat of primer just about as light and third just to get the spots you missed. You should be easely able to see through your primer it should be so thin (not counting fill primer with guide coats and all that jazz for body work). Then light even perpendicular coats of paint for what ever your painting. Again data sheet, time between coats.
After you wrap your head all around that its up to practice of movement with the gun, Sun kissed (orange peal) 100yrd sprints (runs) over spray and cracking.
Have fun!