Use a hyphen after a prefix followed by a proper noun or proper adjective.

Examples: mid-June pre-Columbian Afro-American
Use a hyphen in words beginning with the prefixes all-, ex- (meaning “former”), and self- and in words ending with the suffix -elect.

Incorrect: selfpropelled ex-treme
(Prefix self- needs hyphen. The prefix in extreme does not mean “former.”)
Correct: all-knowing ex-wife self-propelled mayor-elect extreme exacting