I don't empty the colour till after I finished with it, so use a hair dryer to dry each coat of a colour. Then I flush out the airbrush with water, and back flush (water in the paint cup, finger over the spray nozzle, pull trigger back flushes the nozzle).
Then I spray through some Createx Airbrush cleaner
http://www.everythingairbrush.com/ac..._products.html bottomo of page.