If you're going to use water based paints, be sure to clean your brush between coats and colors by shooting some clean water through it, and backflushing, and then do a real good cleaning after each paint session.
I have a tupperware tub full of clean water next to my painting area each time I start painting, so I can just dip the brush into the clean water to flush it between coats. It takes 15 seconds, tops, and I'm ready for another color.
I also made a wire hanger from a piece of coat hanger wire for the side of the tupperware, shaped like a long U with a dropped belly, and ears on the ends to catch the lip of the tupperware tub. I leave it attached full time.
I can hang my brush in it with the tip and the paint bowl in the water, give it a quick backflushing, and I don't get tip dry or paint skinning in my brush between colors, or while I'm heat setting my paint.
I have forgotten and left paint in my brush overnight, and I had to disassemble the entire brush, soak it first in acetone overnight, and then in air brush restorer, to get it to shoot right again. The channels that carry the paint are super fine, and it takes forever to get them clear, once they're clogged!
NEVER LEAVE PAINT IN YOUR AIR BRUSH OVERNIGHT!! It will become an expensive paper weight.