Wikipedia:Manual of Style/Text formatting

The following are proposed guidelines regarding the use of various style devices to show emphasis:

• Italics are used for emphasis, but used sparingly.
• The use of exclamation points are discouraged for emphasis except in a direct quote.
• The use of bold is discouraged for emphasis since it is reserved for headings, subheadings, and article names. Bold is also used in biographies for the person's name and alternate versions of the person's name.
• Avoid using "quotation marks" on a single word, or phrase, for emphasis. Quotation marks are to show that you are using the correct word as quoted from the original source. For example: His tombstone was inscribed with the name "Aaron" instead of the spelling he used.
• ALL CAPS are discouraged for emphasis and should be reduced to the title case where each word is capitalized. "WAR BEGINS TODAY" should be reduced to "War Begins Today". This has become the standard for the New York Times in its transcription project. The same rule applies to book and magazine titles. [1]
• Avoid double emphasis such as "italics" and quotation marks, or italics and an exclamation point.