Try LaTeX with Beamer and/or reveal.js. (Also, Beamer's manual is full of good advice on presentations irrespective of the tool you use.)
I loved especially this gem:
> Never, ever reuse a paper abstract for a presentation, except if the abstract is “We show P = NP” or “We show P ≠ NP”.
> 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.