Jiggarks,
Welcome to the forum!!
Darren has exactly the right idea. Note that the darker your primer, the more color coats will be needed to cover it and produce a bright color - this is especially true for whites, yellows and reds.
I almost always use a flat white primer for red, white, orange, yellow and lighter blues. For darker colors, use gray.
Thinning the paint correctly takes practice, but just experiment - I assume you're using an airbrush, just add 1/4 to 1/3 thinner, try it through the gun, and adjust if necessary.
Good luck.