I stir my paint. clean the lid and threads off, and never get stuck caps anymore. I never leave a paint container open longer than a minute or two also.
And the AKAN paints I have now have a nice cap design where the only thing that needs cleaning are the threads. Tamiya and Gunze Sangyo are really good about this as well.
And the newer acrylic paints I'm in love with. Color fast and easy to spray if one works quickly, and takes care. Must clean airbrush throughly and immediately after spraying tho.