I really fancy my best friends twin brother - how can I make him see me ually?

I know my friend won't mind - she's fine about this kind of stuff. The problem is that I have to make him notice me. I don't want to act slutty because we're only 15 and that's just not me. He's nice to me and seems to like me too, but I'm not sure if he see's us as just friends or what? So, anyway, I want to show him I like him. How can I subtly make him notice me in a 'ual' way? To be blunt, I kind of want to 'turn him on' and I know every guy is different but please tell me what turns you guys on. Any answers would be much appreciated - Thanks(: