Good and bad are two relative terms.. what is good and what is bad changes from time to time and place to place..But a learned wise man, or saint can tell you what is good and what is bad for all times for all men. These sayings formed into epics or sacred texts. A good life should fulfil the objective of your coming into this world. Your good life living should give you happiness and should have no repentances at the time of leaving this body. To lead such a good life, many many methods were described in sacred texts like geetha, quoran and bible , zendavista.
More than that, great saints , avatars, seers commented on these truths. All these truths evolved from a single truth. A truth is that exists always at all places.