Since your question is posted in the literature section, I am assuming that you are wanting to focus upon the characteristics of the classic hero. Perhaps the most prolific person regarding the characteristics of the classical hero is Aristotle. Aristotle first defined the characteristics of the epic hero in Poetics (a literary theory book).
According to Aristotle, a hero's deeds needed to be very specific to be considered heroic. Therefore, a heroic deed is one in which the hero challenges and fights a foe who is equal to or greater than the hero in strength.
Outside of that, a hero needs deeds which challenge him, or her, physically, mentally, and emotionally. Without these challenges, the hero cannot grow and the deeds is not deemed truly heroic. A heroic deed must also be voluntary. If the hero does not volunteer, is forced, then the deed cannot be deemed heroic.
Heroic deeds are important to the society as a whole. The hero's actions benefit the society in some way (as in keeping the society apart from oppression or saving the society from challenging forces (sometimes supernatural)). One last qualification of a heroic deed is that the hero need not be rewarded monetarily for the act.