Presentation Slide Guidelines

Don't make the lettering too small
18pt is about as small as you want to go, 44pt is good for titles and 28pt is good for the main text.

Don't put too much on one slide
Six words per line and six lines per slide is a good guideline.

Restrict the number of fonts that you use
Restricting yourself to two, proportionately-spaced fonts plus careful use of bold and italics will cover most of your needs. Underlining is rarely necessary and slides usually look better without it. A good combination is a sans-serif font (e.g. Arial, Univers, Verdana) for the titles and a serif font (e.g. Times New Roman, Century Schoolbook) for the text.

Restrict the number of colours that you use
Two colours will cover most of your needs.