There are also the basic clichés such as "how are you" or the weather at the moment. Or like >>2 said, if there's anything particularly noticeable about the other person (e.g. a witty t-shirt), make a comment about it.
When I start a conversation with someone I don't know well but have reasons to become acquainted with (e.g. new classmates), I just start talking about whatever is on my mind, as long as this is something the other person could relate to. Like, "Did you read the literature for today? I thought it was boring."

See also:
http://www.wikihow.com/Start-a-Conversation-When-You-Have-Nothing-to-Talk-About
http://www.wikihow.com/Start-a-Conversation-with-a-Stranger
http://www.wikihow.com/Come-up-With-Good-Conversation-Topics
http://www.wikihow.com/Have-a-Great-Conversation