start with a clean sheet

cheat sheet

Any summary or quick reference used as a shortcut or reminder, such as an aid for public speaking.

clean as a hound's tooth

Very clean.

clean as a whistle

Very clean.

clean break

The complete termination of a relationship, or an exit from a situation.

clean hands

Freedom from guilt, especially from the guilt of dishonesty in money matters, or of bribe-taking.

clean money

Money that is legally or honestly gained or earned.

clean someone's clock

To defeat someone decisively, in a physical fight or other competition or negotiation.

clean up

To become clean, handsome, smart in appearance, e.g. for a special occasion, especially when it is out of character to be seen as such.