I am no guru.....I started out airbrushing model cars and then had a job as a sign painter (before I went back to school). I still use my airbrush for small jobs but I have never done anything larger than a motorcycle tank (unless you count long rectangular signs). Working with an airbrush you learn to use a lot of effects, but I am still #$%*e with a larger gun.
The best advice I can give you is the best paint job starts with good prep and good post.