In general, spell out the name or term upon first mention and include the abbreviated form in parentheses right after the spelled-out version.
The Cornell Association of Class Officers (CACO) had a meeting this afternoon. CACO is a vital part of the university.
Don’t use periods in most initialisms.
AAD
CALS
CEO
LGBT
MArch
MEng
MFA
NY
PhD
RSVP
TBD
US
Washington, DC
However, use a spaced period for initials in a person’s name.
A. D. White
Also, use a period in the abbreviated suffix of names, but omit the separating comma.
John F. Kennedy Jr.
For more related guidelines, see names of people.