Prov. Cliché You yourself should do the things you advise other people to do. Dad always told us we should only watch an hour of television every day, but we all knew he didn't practice what he preached.
Behave as you would have others behave, as in You keep telling us to clean up, but I wish you'd practice what you preach. This idiom expresses an ancient idea but appeared in this precise form only in 1678. Also see do as I say.