Just follow him around and keep poking him in the arm saying "Hey"......8) OR....maybe you could go up to him and say "Can I ask you something? Is there any specific reason why you haven't asked me out yet?".....8)
Well, I would just make yourself noticed to him! I'm a guy, so try these ideas out:
1. Look at him a lot (if he sees you doing this, he WILL begin to think about you) 2. Try to sit next to/close to him when you can (lunch/class) 3. Talk to him (don't mind twirling your hair/acting nervous, usually guys find this cute, I know I do ;D) 4. Try flirting a bit! Never hurts! (just don't creep the poor guy out, OK?) 4. Basically, be yourself! A guy usually will NOT like a girl if she just is acting to get his attention. If you are turned down, well, guess that's that and it can't be helped! Good luck!