Filling Graphic Design Gaps

Rachel Healey said:

Thanks for all the insight! I actually have some of those books (Slide:ology and Presentation Zen), and they're incredibly helpful.

At this point, I'm keenly feeling a lack of understanding the "fundamentals," as Jerson mentioned above. I feel like I have a decent eye for design, but I don't know what I don't know. I might make some good choices by chance, but I want to make sure I can back up my graphic design choices with solid theory, the same way I can back up my instructional design choices. In my organization, more and more graphic design responsibility is falling to me, and I want to make sure I'm well qualified to handle it.

Has anyone supplemented their reading and experimenting with extra GD courses or certificate programs?