How to pick a font

Every font has a character, or tone, which communicates on a visual level.
Once you are clear on the tone of the message, look for fonts that communicate the same qualities: Is it light, serious, wry, nostalgic, upbeat, spiritual, technical, fun?
There are so many fonts available, but few are good, well-designed fonts.
Use fonts from established type houses such as Bitstream and Adobe. Although they are expensive, these fonts should read well in all sizes and uses, with good letterspacing.
Avoid so-called free fonts you can get from the Internet. Most are terribly gimmicky. Plus, you'll probably have to spend extra time trying to make the spacing between the letters look right.

Font families

Most serif and san serif fonts come with variations of weight (boldness), width (condensed or extended) and italics.
Consistent, clean type is often achieved by staying within a family, especially one with a lot of variants such as Univers.

The Rule of Two. As a general rule of thumb: for unity and clarity, use no more than two font families in a project. Exploit the variations to establish the heirarchy.

You don't have to choose an obvious font, such as a flowery script for a perfume ad or a blocky san serif for auto parts.
The important thing is to serve the values that the text stands for.

next: Tools for emphasis and legibility