Flyboy & creature have given you the best advice so far. Size the airbrush for the size of your work, and YOU MUST HAVE A MOISTURE TRAP in line, especially in high humidity areas. The kind of "detail brush" flyboy pictured is great for large areas & base coats. If you want/need to get into finer detail use the smaller badger or better yet get a Paasche VL type double action (push down you get air, pull back you get pigment). This will allow you much more control than a typical single action hobby brush and will allow you more types of media by having different tips. The compressor should have a tank on it. The tank acts like a buffer so you don't get small bursts or pulses of air out the tip. You need a steady stream of air, so a good size tank is important (20g or more).

With an air brush, slow is better, and cleanliness is next to the perfect paint job (no matter what media you use). Creature's pressure settings & dilutions are bang on. You need to be about the consistancy of milk or just a hair thicker, shoot it in thin even coats & KEEP MOVING. Like building, you get better with practice, but make sure you move your arm & wrist together to make sure the tip is perpendicular to the work surface, move your arm before the trigger & let the trigger off before stopping your sweep. If the tip isn't perp. you'll get an oval shaped spray pattern, with different drying rates. The badger is a good brush to learn on. I used one when I was 13 for my plastic models (got me my 1st job, building display models for a local toy/hobby shop.)

Also, experiment with mask & masking techniques. Get some frisket paper, and some different type of straight edges, circle templates & such. See what happens when you hold the mask off or away from what your spraying, see how to use the frisket for shapes & camoflage patterens.

Good Luck & happy painting.