An interesting article posted by Apple on using accessible, readable typefaces. Many of the suggestions are worth considering, though following them all might feel a little constricting.
“Legibility is an informal measure of how easy it is to distinguish one letter from another in a particular typeface. Several aspects of a typefaces’ (font’s) design significantly impact how legible it will be.
This is a basic guide for anyone who is looking to choose typefaces that will increase legibility in any document.”
