Hi.
That's great you are investing in a few graphic arts courses. As a supplement, here's a couple of books I would recommend. First, anything by "Robin Williams" (not the comedian) is very good for understanding the basic foundamentals of design. In particular, purchase "The Non-Designer's Design Book". It won't teach you how to draw, but it does teach you about typography and composition. One rule I'm able to still retain from the book, is the concept of "CRAP". "CRAP" stands for Contrast-Repeatition-Alignment-Proxity. The book explores each concept in detail.
In addition, buy a book on color theory. It doesn't matter if it's geared towards traditional art or digital, the end result is pretty much the same. Learn about analogous colors, contrast colors, compliment colors, symbolic colors, psychological colors, etc. Color plays an important part in terms of what you want to communicate.
Hope this helps,
DanH