I am currently watching a course at lynda.com on Design 101 Presentation, taught by John McWade.. Everyone who gives PowerPoint presentations should watch this course. A fdw of his rules are:
1. If you are presenting in a light room, it is best to use black type on a white background.
2. If you are presenting in a dark room, use white type on a black background,
3. Forget pre-made templates. They are often pretty, but they are useless and distracting.
4. Always use type that is large enough to be read in the back of your room. I never use type smaller than 28 point.
5. Use one typeface, preferably a sans-serif font. Avenir, Myriad Pro, and Gotham are good. Use medium weight type.
6. If you want to use a serif font, Baskerviille, Century, and Garamond work well.