The Principle of Proportional Ink is a great primer on how to avoid what Carl Bergstrom and Jevin West call "visual bullshit," like this craptacular graph above. The rule is very simple:
When a shaded region is used to represent a numerical value, the area of that shaded region should be directly proportional to the corresponding value. In other words, the amount of ink used to indicate a value should be proportional to the value itself.
They created Calling Bullshit after deciding "the world has become over-saturated with bullshit and we're sick of it." I'm grateful that they stated the truest truth in all of truthdom:
Three dimensional pie charts, such as the one below, are even worse. We cannot think of a situation in which the addition of a third dimension offers anything other than visual bullshit.
Many other examples of visual bullshit in there, so check it out.