Abbreviations should be restricted to situations where they enhance comprehension; that is, when your copy refers repeatedly to a lengthy name or term that has a commonly accepted abbreviation.
Acronyms are abbreviations that are pronounced as a word, such as NASA, CIRES and INSTAAR. Initialisms are abbreviations that are pronounced as a series of letters, such as ATM, DNA and UMC.
Use the appropriate article (a, an, or the) with abbreviations when you would use that article in speech. The choice between using a or an is determined by how the abbreviation is pronounced. You generally do not need an article when an abbreviation is used as a noun.
GPA and SAT are not spelled out. In fact, SAT is no longer an abbreviation; it is a trademark.
Do not use the ampersand (&) as an abbreviation for and. Use the ampersand only when it is part of an official name of a company, product or other proper noun; or on covers and display matter, at the discretion of the designer.
The names of the 50 U.S. states should be spelled out when used in the body of a story, whether standing alone or in conjunction with a city, town, village or military base. Note that the third example below needs semicolons between entries because individual items in the list include commas. Use the U.S. Postal Service format (two letters, no periods) only when you list a full address including the ZIP code. Do not put a comma between the state name and the ZIP code.
Use periods with the two-letter abbreviation for United States. Do not use periods with the three-letter abbreviation for United States of America.