Learning to spray paint

I've assembled my compressor, mounted a regulator/filter, have done
some sandblasting, and done some grinding with my die grinder. Now
it's time to learn how to use the paint sprayer.

I've been spraying water on a cardboard surface, but the viscosity/
volitility of water is such that I fear I'm not getting much out of
the exercise.

My end objective is to spray 2-part epoxy primer, but that's expensive
to learn on.

Any suggestions on an inexpensive medium to practice with? Enamel
diluted IAW directions? Interior housepaint? - Mike