Use sans-serif fonts, such as Helvetica, when using a projector. Serifs look fuzzy. Use only one sans-serif font. Don't use italics unless necessary. Use white text on dark background or dark text on a light background.
Size does matter Presenting from a laptop is much different than using a projector.
A 1-inch letter is readable from 10 feet. 72-point fonts are 1 inch high. If you can, know the room you will be presenting in ahead of time and adjust as necessary. Don't sacrifice readability for style. Don't bury your text in between pictures and under animations.