Just walk up to her and start making out with her after 4th period at her locker. That would go down in school history as the coolest thing that has every happend. . .ever!. . If that's not your cup of tea. I would wait until she is in a conversation with some people that you may know. Then walk into the group and try to work yourself into the conversation. Be sure you know something about the topic and can add value so it's not just an awkward moment. Then just say "What did you do last weekend?" Or "Hey (insert her name) what do you usually do on the weekends." . . The whole group thing helps it not to be some wierd awkward moment where you try to sit next to her at lunch or catch her in the corner of class. Talk when others are around and talk in generalities. Kind of feel her out. Ask her questions about her and let her know a little about you. Don't be too aggressive and be all "Hey I want to be your friend" b/c that freaks people out.. . Or my original suggestion always goes over in certain social circles :)