The most important quality according to me would have to be....

a good listener when I need one. I'm a good listener, and I try to give back good responses, not just "uh huh, yeah, I understand, yeah..." I try to say more than that. And the people (not naming who here) I call my really good, close friends are the ones that know who I am and listen to all I say, and even ask me questions.

It means they're interested in the friendship they have with me.