I found that the most helpful part of this chapter was the explanation of simplicity and clarity. While it may seem obvious, I've always been told throughout my years in school that after completing a chart or graph I should strive to make it look nice, and that cluttered information is a bad thing. This book kind of redefined that for me, as it showed me information graphics that I would tell you are horrible. Most of the time I've been told that the objective should be to give the audience an information graphic that they can very quickly look at and understand completely with little thought involved. Tufte corrects that misconception, explaining that clarity and simplicity are to be valued, but that the more information that can be represented most easily, the better, and that artistic flair often gets in the way (which for someone who is terrible at art, is nice to hear).
While this may have nothing to do directly with how to setup an information graphic, I still feel like it was the most useful portion of this chapter, because it may help me correct problems that otherwise naturally occurred when I set up information graphics.