Well, I'd try to have a conversation and crack a few of my jokes and see if theyd laugh (if they dont, I wouldn't consider them) Also, if they're a player or not (roommate getting lots of girls but YOU not getting lots of girls can be REALLY annoying!)
I'd try to see if they're calm people with things in common with me. Because I get along with calm people.
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You are a part of the world, and the world is a part of you.