Echo washing the plastic thoroughly. There's always residual dirt and oils that prevent paint adhesion.
Second, I use Krylon Fusion for a base coat. I airbrush my paint jobs because the layers go on thinner. Enamels cover better, but scratch easier. Acrylics require a couple of coats for maximum coverage, but endure wear and tear MUCH better. Best practice for me has been shoot the colors in enamel and then use an acrylic sealer to prevent scratching. Testors ClearCoat is fine, gloss or flat. Gloss dries slower, but airframes look more realistic. I generally like using the Acryl clears out of an airbrush for the same reason I only use Fusion for a primer coat, it goes on thinner and doesn't run.
Acrylic paints dry FAST. REALLY fast, so you better have the paint exactly where you wanted it. The good news is that after it dries, you can do touch-ups pretty soon after. Enamels require about 24 hours drying time before they can be safely handled. Also, the thinners associated with airbrushing enamels are pretty dangerous to inhale. Respirators are a must. Acrylics are safer, but you still probably don't want to inhale atomized plastic. A lot of acrylics can be shot right out of the bottle, but you can thin them very easily, Windex is best. It should be as opaque as milk.
Brands? Start cheap and get fancy after you've gotten some experience. Model Masters Acryl works great, doesn't require thinning. Tamiya acrylics do, but they look really good. Enamels? I love Humbrol, but it's expensive as hell.
Most of all, do exactly what you just did: ask questions. There's guys in here who have been customizing figures and vehicles since the first Reagan Administration. I am a rank amateur compared to the guys in this place.
