How do I become friends with people I don't know without looking stupid?

I'm going to a band concert, and the people are from other schools. I don't know them at all. I'm scared to say hi because they might say ,"I don't know you, so why are you saying hi?". I don't want to say what's up, because I have a reputation for being intelligent. To rephrase, how do I greet people first or start a conversation? I am socially inept.