[lufttiger]

This depends on the paint your using, enamals can be your worst enemy
in an airbrush if not used right. I myself no longer use them in my airbrush.

I use acrylics, which i use an eyedroper to gage my amount.
I usually dilute it one part paint to on part rubbing alcolhal, you'll have to test
to see where its best for you.

If it looks too dry on the model: you've diluted it too much

If it flows slow, and clogs, then not enough diluted

Hope this helps