Before spraying the paint I run some Windex thru the air brush, and use about 12 PSI air pressure.
I do use the "regular" paints rather than the Model Air type. I have read here and elsewhere the Model Air paints don't give as good results.
I also clean the resin parts with Easy Off spray oven cleaner & prime with a sandable spray primer, just what ever brand is on the shelf at the auto Zone.
I thin the paint 2 to 1 with a blue Windex type window cleaner and mix well.
I've read here that it's the ammonia in the window cleaner that does the job, but I haven't tried using straight ammonia.
So far the paint has stood up to handling while building the models, but you can't sand it, it will clump up & roll off.
Hope this Helps,