If he's a friend...
You hang out with this boy on a regular basis, you have lots of the same friends, and may even talk on the phone or IM, but he has no idea you're crushing on him...
Set it up: Start giving this cutie some extra attention. When you're with the gang, make it a point to be near him. If you're sitting at a table, take the seat across from him so you can send him a flirty smile. Casually touch his arm while you're talking or give him a friendly little nudge in the hallway between classes (but don't overdo it).
Make your move: The next time your crowd is at the movies, ask him to help you with the popcorn and sodas. Once you're one-on-one with the boy, say something to let him know you've been noticing him, like, "Hey, that was a great speech you gave in class."
Ask the question: Call him when you know he won't be busy. Asking over the phone can give you a bit more courage because you're not face-to-face. If no one answers, do not leave a message -- waiting for him to call back is unnecessary torture. When you do get him on the phone, ask him to do something specific that you're both interested in, like, "I'm on my way to the skate park. Wanna come?" If he starts acting weird, mention that some of your friends will be there and it's no big deal if he can't make it. Then call some gal pals and head to the park (if he shows up, you won't be a liar!). Yeah, you'll be bummed if he bails this time, but if he says yes, you've got yourself a date!