Abbreviations and Acronyms
"Some widely known abbreviations are required in certain situations, while others are acceptable but not required in some contexts. For example, Dr., Gov., Lt. Gov., Rep., the Rev. and Sen. are required before a person’s full name when they occur outside a direct quotation. Please note, that medical and political titles only need to be used on first reference when they appear outside of a direct quote. For courtesy titles, use these on second reference or when specifically requested. Other acronyms and abbreviations are acceptable but not required (i.e. FBI, CIA, GOP). The context should govern such decisions.
As a general rule, though, you should avoid what the Associated Press Stylebook calls “alphabet soup.” Consult the Associated Press Stylebook for specific cases."
Credit: Owl at Purdue, Associate Press Style