Well that is a good question. What airbrush you running and what needle set up?
What paint and what air pressure?
Most times if I am pulling a really tight line my air pressure is around 5 to 10 psi. my paint is reduced 1 drop paint to at least 15 drops reducer (if I am using wicked ) pretty much straight out the bottle if I am using Spectra-tex
That is with my Iwata Eclipse CS with a .35 set up.