How NOT to look mean, standoff-ish and loner-ish?

Body language says a lot about a person. Don't stand around with your hands in your pockets or your arms folded across your chest. Stand up straight, be a "presence". SMILE, look people in the eye when conversing with them. Be a good listener. Act interested. Be outgoing. Join an after school club. Greet people using their name. Good luck.