I've just spent a few weeks learning how to use an airbursh the hard way. I looked at many sites for info including this one and thought I'd try to help people like me with one I hope easy to understand post (I'm from England so if I use terms or spelling sure you can get past that)
1, Spend as much as you can on the Airbrush, I baught a cheap one from ebay to learn on and didnt learn anything as I couldnt use it. You can save money else where trust me please! I now have a Badger 200 I'm not saying its perfect or you shold get one its just what I have.
2, Paint thinning, I use 2 parts paint 8 parts thinner. I know a lot will say thats too thin but its easier to do more layers than less. I also use Tamiya paints so use Tamiya thinners. I've tried all sorts in the part few weeks from water to the propper thinners so again trust me if you can on this use the thinners your paint manufacturer produce. I use a lot of thinner but then it costs less than paint
3, Extra items I use are in order I use them. First cheap syringes, I baught these from Ebay so its easier to measure the paint out and just throw them away after, thinner in the feed jar first then the paint after. Next use a mask and eye protectors, buy once and never be sorry. First time I cleaned my airbrush with a can of airbrush cleaner I almost got the cleaner in my eye and after that I was wearing eye protectors(you only get one set of eyes after all).
4, To learn how to really paint the best advice I have is buy old cheap kits and work at it. I didnt even take any parts off the pruces. Start the paint before the part to be painted keep it going till just after. You loose a little paint but it looks much bette, keep the same distance from the parts.
I hope this helps as a little advice to novices like myself. If anyone else has more to add please do as I'm no expert but I'm learning and getting better every time I try.