To avoid wasted effort, it is important that you begin working on your mockup as early in the design process as possible. Given the importance of the graphical element, you will want to take special care that your graphics are both easy to interpret and data-rich. Among Tuft's most important contributions to graphic excellence is the notion of data-ink ratio. Excellent graphics have high data-ink ratios. All these effects, while superficially flashy, merely make it more difficult for the viewer to extract the information you want to convey in your poster.
Excellent graphics are data-rich.
Your graphics should portray as much of the detail in the underlying data matrix as clarity allows. For example, if you want to compare sherd thickness in a suite of ceramic assemblages, give some thought to how you might portray not just summary measures like means and standard deviations, but shapes of frequency distribution or perhaps even individual data values. Data richness lends credibility to graphics. It also offers openings for your audience to respond to your presentation. Data poverty not only provides very little basis for dialogue, but may leave the viewer wondering about the quality and quantity of your data.