The Catechism goes on to identify three essential elements of which the common good consists: "respect for the person as such"; "the social well-being and development of the group itself"; and "peace."
Fr. Albert Nolan, O.P., in a homily preached on Human Rights Day 2007 in South Africa (here's a link to the audio), gives a succinct description of the common good:
... what is best for me is what is best for everyone. And if we can see what is best for everyone, then that is what is best for me. This is what we call "the common good." This is also the will of God.
If we can get to the point where we really see what is best for us being what is best for everyone, and vice versa, then we can get to the point where the common good is achievable. To do that, though, we can't settle for the easier goals of individualism or collectivism.