Empty the paint cup of excess paint by turning the airbrush upside down and pouring the paint out into a trash receptacle or back into its bottle. Spray out all excess paint from the shaft into a bucket or trashcan. Keep spraying the paint until nothing comes out but clean air.
Wipe out any paint that has stuck to the sides of the paint cup of the airbrush by wiping the cup's walls with a cloth or paper towel. Stuff the paper towel as far down into the paint cup as you can to soak up some more of the paint. A small paintbrush dipped in rubbing alcohol can be used to get into the smaller areas.
Flush out the airbrush by spraying clean water. This will dislodge large chunks of paint from the airbrush's shaft and nozzle. Fill the paint cup with clean water, then spray it out. Repeat until the water comes out completely clear.
Clean out the airbrush with alcohol or airbrush cleaning fluid. Use one of these chemicals to clean out the airbrush when you don't plan to use it again for a while (after a painting session, for example). Fill the paint cup with one of these solutions and spray it through.
Dismantle the airbrush and clean each part individually before prolonged periods of nonuse. Unscrew the nozzle and back end of the airbrush and remove the long needle. Soak all of the parts in a solution of water and rubbing alcohol for a few hours before reassembling the airbrush.