A poster figure is not a paper figure. It has to work at a distance, quickly, under bad lighting.
- Axis labels with units, always. "Mass (g)", not "mass". An unlabelled axis is the most common single defect on fair posters.
- Show the uncertainty. Error bars with a caption saying what they are — SD, SE, or 95% CI. Bars without that caption are ambiguous and judges will ask.
- Show the data when you can. With small n, plot the individual points over the bar or box. A bar chart of three values hides more than it shows.
- One message per figure. If a figure needs two sentences to explain, it is two figures.
- Type no smaller than 20 pt in the printed figure. Export at 300 dpi; a chart that looks fine on screen can be unreadable in print.
- Do not rely on colour alone. Roughly one in twelve men has a colour-vision deficiency. Vary shape or pattern as well, and avoid red/green pairs.
- Start bar-chart axes at zero. Truncated axes exaggerate differences and a judge will notice.
Final check: print it, put it on the far wall, and read it from three metres. Anything you cannot read gets bigger.