I assume you mean the thinning ratio when you say "Paint Mix". If I'm wrong, please let me know.
It's going to depend on your situation. The paint viscosity, your airbrush, and air presure all affect how thin the paint should be. With enough pressure you could get motor oil to go through an airbrush. You need to find the point at which paint will spray properly through your airbrush at the pressure that you like to spray with. Generally speaking your paint should be about as thick as milk.
I spray Tamiya paints thinned 3:1 (3 parts paint, 1 part thinner) at about 15 psi. If you use more pressure you can use less thinner. Find the ratio that covers well when you spray it and doesn't require a lot of pressure.