Well I discussed a bit on getting started if you have drawing abilities.  But if you are a little lite on the drawing part of it it disn;t mean your out of the airbrush game.  With computers it is easy to design and print out your own airbrush stencils.  You can pick up Photoshop CS3 a lite version of Photoshop for around a hundred dollars.  Or you may already have less sophisticated app to re size crop and composite photos and artwork in your computer.  Many times they are bundled with you printer software. You can use an online photo editor to create your stencils.  A good one I found is at  http://fotoflexer.com/

You can then print out the design you have created and using an xacto knife cut out you stencil from standard paper.  This can be used as a lite stencil.  You just want a lite shape, you don't want any hard edge build up.
So you can get by with less ability, but my best advise is to practice practice and more practice. Airbrushing is an art form and must be understood as so. 

Many get the idea since it is a spray gun it is like using a spray gun to paint a house or car.  The better the artist you are, the better the finished project will look and the better the chance you will succeed becoming an airbrush artist.