Boldface should be used strategically, as little as possible.

Use bold fonts to emphasize and/or highlight important points or UI features.

If everything is emphasized, then nothing stands out.

Use bold type to slow down your reader; it causes your reader to take in the words more carefully.

Bold fonts are also an excellent way to create contrast.

Use bold fonts to increase the contrast between the headline or header and the body text.

Use bold fonts to aid the skimming of instructional text.

Boldface fonts can aid the reader's skimming. It can be useful for readers to have titles, proper names, or key terms highlighted.

To emphasize text, bold should be used, not italics.

As a rule of thumb, you should not use both bold and italics together.

The only exception would be if you need to emphasize a word or phrase within a bolded section.

For the most part, you should avoid using italics for emphasis.

If a portion of text requires emphasis, it is best to rewrite your sentence to provide the emphasis where it is needed.

One way to do this is to place important words or phrases at the beginning or end of a sentence instead of in the middle of the sentence. You can also break long sentences into several shorter sentences.

You should use italics if the emphasis will be lost with a rewrite of the sentence(s) or if the text will likely be misread.

Do not use italics for company names and brand names.

Common Applications for Italics:

The first use of key terms or phrases, often accompanied by a definition.

Regardless of font style, Dozuki recommends definitions be kept in their own section of the document.

Titles of books, reports, webpages, and other stand-alone works. See the Big Things, Little Things titles guide.

Anchors of a scale (but not the associated number): ranged from 1 (poor) to 5 (excellent)