Prep work is the most important phase in any model building. Painting is easy. Sanding, priming, re sanding, re priming, and repeating is tedious work but in the end, it is well worth the effort.
Once all this is done, the final primed surface is wet sanded with a very high grit sand paper, I used 4000 grit. What this does is that it gives the surface as smooth a surface for the paint. When paint is sprayed onto the surface, it will inherit all the tiny bumps, imperfections, settled dust, etc that lies on the surface. Wet sanding prior to painting ensures that the surface is a smooth as possible, which make the paint application that much easier.
More information here: Habanero Tan Progress Page