A precept is a rule or direction, often with some religious basis, dictating a way you should act or behave.
Precepts are little life lessons that are usually passed down to children by authority figures such as parents, teachers, or religious figures. They are not as simple or practical as "eat your vegetables"; they tend to be more weighty and pretentious. In Hamlet, the character Polonius dished out a few choice precepts to his son Laertes: "neither a borrower nor a lender be" and "give every man thy ear, but few thy voice." Of course Laertes never lived long enough to benefit from Polonius's sage advice, since Hamlet offed him with his own poisoned blade.