Use abbreviations and acronyms only when they will help your readers by making written text simpler and less cumbersome. Do not use an abbreviation or acronym that would confuse your readers, that they would not recognize quickly. When in doubt, spell it out. (An abbreviation is a shortened version of a word or phrase, like Mr. and Corp.; an acronym is an abbreviation formed from the first letter or letters of a series of words, like AIDS, Garbl, NAACP and radar.)
Always spell out terms, common names and the complete proper names of organizations, projects, programs or documents the first time you use them, and repeat the complete term or name at the beginning of sections in longer documents. Although the abbreviation or acronym is capitalized for some common or generic nouns and terms, lowercase the spelled-out form.
If an abbreviation or acronym of the term or name would not be clear on second reference, avoid using it. Instead, use a shortened version of the name or a generic word, such as the agency, the committee, the department or the company.
If using unfamiliar abbreviations and acronyms is necessary, follow the complete name with the shortened form set off between commas: The Endangered Species Act, or ESA, affects many projects. Later references could use the abbreviation, a shortened version of the name or a generic word.
Whenever possible, avoid following the name of an organization, project or program with an abbreviation or acronym in parentheses or set off by dashes: Endangered Species Act (ESA).
Do not provide an abbreviation after spelling out a term if the abbreviation isn't used elsewhere in the document.
Omit periods in most abbreviations and acronyms unless the result would spell an unrelated word. Use only one period when a sentences ends with an abbreviation that includes periods.
Don't use the before acronyms pronounced as words instead of letter by letter: OSHA, CAD. With other abbreviations, apply the same rules for the full name and the shortened version: the ESA, the state DOT, IBM. When placing either a or an before an abbreviation or acronym, determine how it would sound when spoken; see a, an, the entry above.
To form most common plural abbreviations, add an s: ABCs, CDs, chaps., Drs., IOUs, TVs, UFOs. Sometimes, an apostrophe may go before the s: when the abbreviation has internal periods (M.A.'s, M.B.A.'s, Ph.D.'s), when the abbreviation is composed of lowercase letters (pdf's), when the abbreviation is a single letter (A's, S's) and when the abbreviation would be confusing if only the s were added (OWS's instead of OWSs). In the last example, if your readers might misinterpret an abbreviation like OWS's as showing possession, leave out the apostrophe.
Avoid using e.g., i.e.; et al.; etc.
Many abbreviations may be used in charts, tables and certain types of technical writing.
If the meaning is clear, abbreviations may be used in headlines and headings.