I used to teach a class in data visualization because I was frustrated with the quality of graphics in student work and that I was seeing in papers I was reviewing for journals. I just saw an article from my colleagues at Penn State that provides an excellent overview of effective data visualization principles. The article is about a year old now, but you will find it useful…I promise! They draw on theory from cognitive psychology and experts like Edward Tufte and William Cleveland. Personally, I know I could benefit by using these principles more often in graphics that I create.
Kelleher, C. and Wagener, T., 2011. Ten guidelines for effective data visualization in scientific publications1. Environmental Modelling & Software, 26(6): 822-827.