If the abbreviation is being used in formal writing, it will need to conform to the Associated Press Stylebook. If the abbreviation is being used in a song, it is important to understand the pronunciation, which is always "mike," regardless of spelling.
Consult the Associated Press Stylebook. In 2010, the AP Stylebook, which is used by major newspapers and other publications, changed its rule for abbreviating microphone from "mike" to "mic."
Choose between the two standard abbreviations. Mic is used by those who follow the AP Stylebook and are generally in the technical or music business. Mike is used by more traditional writers.