Which four qualities do you look for in a friend? On my Mt. Rushmore, the first two qualities are chiseled in the hardest rock, my Washington & Lincoln - i.e., "must haves" for any friendship. The third & fourth are marginally less significant, my Jefferson & Roosevelt.
1.) Trustworthiness: I want my friends to know they can rely on me. If they tell me something is for my ears only, they can depend on me to keep my mouth shut. I expect the same in return.
2.) Sense of humor: No laughter = no friendship.
3.) Adventurousness and keeping the "those were the good old days" rhetoric to a minimum: In my experience these two qualities go hand-in-hand. I want friends who'll try new foods, new experiences, new music, new places, new authors. Old stuff is fine but let's get some new into the mix, shall we?
4.) If someone is a parent, an unmistakable recognition of the value of that experience. Although parenting can be a gigantic pain in the ass at times, I give wide berth to people who continually complain about their children. For me, a friendship with someone like that is likely not in the cards.