Mike Taylor shares 4 tips for visual design for elearning: alignment, visual hierarchy, less text, and animation. Even if you have no graphic design background, you can learn some basic tips like this to improve your design.

Theory of visual language (h/t Kevin Thorn). "Visual language research can hopefully provide insights into how we understand, teach, and use drawing and visual narratives..."

Tim Slade explains basics of visual design for new elearning developers, focusing on picking fonts, colors, and images, plus creating slide layouts.

While these examples are all websites, the design principles apply to elearning too.

Bryan Jones demonstrates the design principles of CRAP (contrast, repetition, alignment, and proximity) by taking some boring, text-only slides and gradually improving them.

18 "laws of UX": principles of user experience and how people interact with sites and online content. Some of this is visual design and visual communication; some is interaction design. I'm not sure that the Pareto principle is really a UX law, since it applies in many other situations, but you can stretch the definition a bit.

Some basics of color theory and how to create color palettes

Do people spend more time reading large or small type? More time looking at large or small images? Is animation the best way to show changes over time? Summary of common questions/myths with research answers