One of your best – and funniest – primers on the use of fonts is waiting for you at Cracked.com. On their Fonts topic page, they’ve got a collection of discussions, photographs, and links to other articles, that will cover much of what you need to know. Be sure to keep reading, almost to the bottom, so you don’t miss anything.
And by the way, some of those pictures appear not to be Work-Safe, even if, technically, they are. But that’s exactly the sort of mistake this page is demonstrating: what can go horribly and inadvertently wrong if you don’t pick your fonts carefully. And wait till you see the picture of the bulletin that probably contains most of the fonts ever made…
Usually the best rule for choosing fonts for your document is simplicity. And readability is kind of a subset of that. Some people have suggested that the easiest font to read on a printed page is Times New Roman, because it is a serif font (that is, it has those little extra nicks at the tops and ends of the letters), while Arial or Helvetica are easier to read on a screen.
Another rule seems to be that you stick with one font for everything on the page, or at most, have a second font only for things like headings and titles. And even then, they shouldn’t be wildly different or the incongruity will be glaring.
Does this sound boring? It might, but remember that your main goal is always to communicate clearly. If people are spending their time trying to discover what letters are contained in the midst of all those swirls and angles in your text, you can be sure they’re not actually getting your message. Which rather defeats your whole purpose, doesn’t it?