There are a few different ways to approach this, and I’m all too familiar with your pain, as rules of design wasn’t anything I thought about when I started down this road.
Couple of approaches you can take. One is to find a good graphic designer and just ask questions. We worked on a few projects together and I have learned quite a bit from him, about the basic rules of graphic design.
Also there are tons of books that can give help you understand the more formal rules of design, two that I recently picked up might be a good start.
The Elements of Typographic Style
Making and Breaking the Grid: A Graphic Design Layout Workshop
Got both used at amazon, understanding typography and basic layouts, while not required in this business, will IMO, elevate your work to more aestically pleasing levels.
Johnny Cuevas, Editor
http://www.ckandco.net