Graphical excellence is that which gives to the viewer
the greatest number of ideas
in the shortest time
with the least ink
in the smallest space ...

Five principles produce substantial changes in graphical design:

  1. Above all else show the data.
  2. Maximize the data-ink ratio (i.e., the % of ink that shows data).
  3. Erase non-data ink.
  4. Erase redundant data-ink.
  5. Review and edit.
.... Computers can do powerful things graphically, in part by turning out the hundreds of plots necessary for good data analysis. But at least a few computer graphics only evoke the response, "Isn't it remarkable that the computer can be programmed to draw like this?" instead of "My, what interesting data" ... Forgo chartjunk.

(Edward Tufte, The Visual Display of Quantitative Information)