Cleaning your brush often, after every color change, is, for me, one of the big keys to trouble free air brush painting.
I'd suggest you have a tupperware full of clean water next to your painting station, some rags, and a spray bottle with water and a couple of drops of dish washing liquid mixed in.
When you finish with one color, drip the excess paint back into the paint bottle, wipe out the brush's bowl with a rag, dip the bowl into the clean water, and back flush it well. Do that several times. Then use the soap/water spray bottle to fill the bowl again, back flush well, and clean out the nozzle with a soft brush and the soap solution.
Take the needle out and wipe it clean. Then put it back in CAREFULLY. Bent needles are a nightmare.
Then flush one more time with water, and you're ready to paint again.
Once you develop a routine, it doesn't take long, and it will help avoid lots of the problems we all encounter with air brushes.
Have some acetone handy, and use it to backflush your brush once a week or so, and it will keep the paint from building up in the tiny air holes around the nozzle.
Depending on the paints you use, how hot it is, and how much you thin your paints, you may find you need to do the cleaning routine more or less often. I do it a lot, and don't have to do an acetone cleaning very often at all.
I do use a spray bottle of Windex as a part of my cleaning routine, with a backflush with Windex between the first water backflush and the dishsoap flush, but some people say Windex, or at least the ammonia in it, attacks the chrome of the air brush. I flush it all out so well I don't worry about it, and the ammonia is good at breaking up any dried paint.
The other key is thinning whatever paint I'm using to the consistency of skim milk, and just using more coats, with each coat heat set with a hair dryer. Use whatever thinner the paint manuf. recommends, and you won't go wrong.