All answers above will work great but I find going the Alcohol route the preferable choice for myself.
Isoproply Alcohol (Rubbing Alcohol) is the cheapest and easiest way I have found to clean the Airbrush of Acrylics. Plus it gets it off your hands without burning like Lacquer thinner and other cleaners do. Thus no gloves required! You can find decent size bottles at the dollar store. Lacquer thinner is what I use to clean enamels and Lacquers only. Just due to the cost of it.