Q: How often should I lube my airbrush?

A: As often as the airbrush needs it, but not so often as to get lube into your paint.

In-Depth

It's not really a question of schedule like changing your car oil every 3000 miles.  There's only two places on an airbrush that require lube and an optional set of locations.

• The Needle Packing O-Ring

  The piece, deep inside the airbrush, needs just a little lube to let the needle pass through it without problems.
   
  
  Notes: Teflon Needle Packing O-Rings don't need lube, but the action still tends to feel better if you do.

• The Air Valve Packing O-Ring

  This o-ring seals the air system from the trigger housing.  The air piston, or dangly piece underneath the trigger depending on your model, needs just a little lube to let the trigger spring up and down nicely.
  

• Screw Threads

  Screw threads don't NEED lube.  In fact, I prefer beeswax since it's natural, but lube works too.  It works as a temporary, non-drying sealant to keep various kinds of leaks from happening.  Not to mention it 'feels' better to screw things together that have a little lube between them.