Basically, the idea here is to figure out your best strategy for the 'game' (which really means any situation where you need to make a decision), given that the other "players" don't cooperate with you in any way (i.e. you assume they are going to act in their own self-interest).
The most basic successful strategy for the Prisoner's Dilemma is called "Tit-for-Tat", in which you always choose the "altruistic" option, unless the other player chose against you last time.
Follow that up with the EconTalk podcast episode with Dr. Bruce Beuno de Mesquita: http://www.econtalk.org/archives/_featuring/bruce_bueno_de_m...