Introduce yourself. This is the simplest way to talk to your crush, but simplicity is often key in these situations. It's easy to say "Hi, I'm [your name], what's your name?" This will make it easier to talk to him in the future because rather than just being a face, he is now a name as well.
Ask him questions that lead to discussions about his interests. Rather than ask "What kind of music do you listen to?" you could say "I just bought this CD, what do you think?" This keeps your conversation from seeming like an interview and makes it flow more effectively.
Tell him a story about something that relates to him. The connection needs to be clear -- if he's reading a book, and your Aunt Francie loves books, don't tell him a long story about Aunt Francie's cats. However, if you have the same teacher in a class, he will probably appreciate a story about that teacher.
Ask him about his clothes. This will create conversation about what kind of clothes he likes and where he gets them. It will also give him an opportunity to talk about himself, which everyone likes to do.
Answer his questions when the tables turn. It's not fair to insist that the conversation revolve around him, which could make him nervous or creep him out. Provide information about yourself when asked, so you can converse about shared interests or find areas you have in common.