• Talk to the audience not slides
• Whenever you show a plot, start by explaining the axes and what is being plotted.
• Plots should standalone, caption, title or annotate them, so that any subsetting or summarising is made clear.

Readability of plots:

• Don't be afraid to devote an entire slide to a plot. If you can't read one, then don't put on more than one.
• Axis labels need to be bigger ( I use + theme_bw(18) in ggplot2 to increase the base text size to 18pt)
• Beware pale colours with projectors (especially yellows) they tend to disappear.
• Save plots as pdfs, unless the file size is large, then use with png with at least 300 dpi.