How do you get to know someone better?

Don't interrogate them, but try to get them to open up about themselves. Casually ask about their job, their family and friends. What kinds of things do they do in their free time? Discuss hobbies, what kinds of music/movies/books they prefer. Be honest about yourself and what you enjoy in life. Note these things: Do they complain a lot? Have they changed a lot of jobs/moved frequently over the years? Do they say rude things about their parents or ex girlfriends/wives? Any of these could be a warning sign.