Mix ratio for Tru-colors paint?

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I've been working on some F&C kits lately. Got to the point for painting and figured I'd give Tru-colors paint try again(They had the prototypical color for this particular boxcar). Tried paint directly out of bottle in my air brush as stated it can be used. Paint came out dry and caused a rough surface( I should have experimented on a scrap piece of styrene or something. Lesson learned). So, boxcar has been stripped and I am preparing to paint it again. 

Anyone use Tru-colors a on a regular basis and have a ratio for paint and thinner that seems to work well? I did pick up a bottle of Tru-colors thinner, so I have that on hand.

Thx,
Mark