The beamer package manual had nice hints, like ~1 page just about font size. With statements like
> In beamer, the default sizes of the fonts are chosen in a way that makes it difficult to fit “too much”
onto a slide.
Many of the ideas apply outside of latex/beamer. It's one of the better free documents about the technical aspects of slides. At least if the presentation is still driven by content on the slides, but that decision is a whole different story.
