Three things are necessary for the salvation of man: to know what he ought to believe; to know what he ought to desire; and to know what he ought to do. (St. Thomas Aquinas)

I find this a very efficient three-step guide to living, provided of course that we interpret "ought to" in a way that is very much not the Angelic Doctor's.

(For the record, he followed up with: The first is taught in the [Nicean] Creed... the second in the Lord's prayer; the third in law. Wish it were so simple.)