Oh man. I don't think there's a simple answer to that question. In my experience, the more I understand myself and the type of people I like being around, the easier it is to identify them when I come across them. That makes it sound intellectual, but really, it's more of a gut thing for me—and the better I get at noticing positive or negative (or neutral) feelings toward someone in the moment, the easier it is for me to invest in the people that seem like the most natural fit. It's a slow and iterative process, in my experience.