I'm not an expert when it comes to airbrushes, so take this for what its worth.
First off, I never use the standard paints I use for painting with my standard brushes. A few people suggested watering the paints down and adding dish detergent. I have tried and it never worked for me.
I have 2 air brushes (and they are old) I have a Badger single action, which is good for big jobs. Such as base coating mainly. I used this one on a Tau job I once did for somebody.

Did all of those with an airbrush. It beats buying cans of paint or spending hours brushing the base coat on.
Final Product -->

Then I have a Double Action airbrush (Paacshe) which gives better control when it comes to flow of paint and laydown. You can do anything from pencil thin to thick broadlines a bit easier than with a single action airbrush. I use this for camo work or anything which requires a soft blending of color.
Here are a couple of examples:
All the pics above were done using GW and Vallejo paints (thinned down of course). My problem is they always seem to clog the nossle. Which then requires cleaning (I hate cleaning!!)
There are other brands of airbrush out there (Aztek), and pretty cheap. There are some which do not have a needle and clean really easy. They are also inexpensive.
Here is a link which you may find helpful
The airbrush - which one to get and how to use it
Hope I was of some help.