Summary Recommendations

In general, avoid bar plots
Avoid chart junk and the use of too much ink relative to the information you are displaying. Keep it simple and clear.
Avoid pie charts, because humans have difficulty perceiving relative angles.
Pay attention to scale, and make scales consistent.
Explore several ways to display the data!

12 Tips on How to Display Data Badly

Adapted from Wainer H. How to Display Data Badly. The American Statistician 1984; 38: 137-147.

Show as few data as possible
Hide what data you do show; minimize the data-ink ratio
Ignore the visual metaphor altogether
Only order matters
Graph data out of context
Change scales in mid-axis
Emphasize the trivial; ignore the important
Jiggle the baseline
Alphabetize everything.
Make your labels illegible, incomplete, incorrect, and ambiguous.
More is murkier: use a lot of decimal places and make your graphs three dimensional whenever possible.
If it has been done well in the past, think of another way to do it

Stephen Few: Designing Effective Tables and Graphs. http://www.perceptualedge.com/images/Effective_Chart_Design.pdf
Gary Klaas: Presenting Data: Tabular and graphic display of social indicators. Illinois State University, 2002. http://lilt.ilstu.edu/gmklass/pos138/datadisplay/sections/goodcharts.htm (Note: The web site will be discontinued to be replaced by the Just Plain Data Analysis site).