Dear Jellybean,
Ok. I definitely know who I like. The problem is, he's already taken. After the two break up, I'm going to ask him out. Let's say, asking guys out isn't my forte, and I'm pretty new at it. I don't know what to say, when to say it, how to act, what to wear, I know nothing. This guy is friends with me, but we never hang out (outside of school) and I never call him.
Dear Writer,
You've got the beginnings of a plan - you know who you like, and what you want (to date him). Now it's time to work out some details.
If you never hang out with your crush outside of school, and you never call him, it could seem awkward or blunt to just ask him out, as soon as he becomes single. A better strategy would be, to take advantage of this "just friends" time (since you shouldn't go after him until he does break up with whoever he's dating) by deepening the friendship.
How do you accomplish that? You could try a few things. Whenever you're going to hang out with a group of guys and girls, say on a weekend trip to the movies or the mall, or a party at a friend's place, invite your guy friend to come along. Of course, make it clear that his girlfriend is invited too, or he might skip it. This isn't sneaky or devious, as long as your only intention is to get to know him better as a friend, outside of school.
You can also try to get to know him better at school, by taking conversations a step further. If now you just say "Hi, how's it going" when you see him in the hallways, try to get real chats rolling. Ask him about what he did on the weekend (or what he's got planned for the coming one), if he's heard a popular new song, what he thinks of a class you both share, etc. The more you talk to each other, the better friends you'll become, and he'll get to know what an interesting person you are.
If and when your intended does break up with his girlfriend, you can make your move. I advise subtlety, rather than moving in for an obvious attack. As in, don't just ask him out. Go for the "supportive friend" role, by telling him you're sorry things didn't work out for his relationship, and you hope he's feeling okay. Offer to hang out anytime, if he feels like just doing something fun and distracting himself from any hurt feelings. You could even leave a friendly note in his locker, saying "I just want you to know that you can call me anytime to talk" or words to that effect.
What you shouldn't do is, dress provocatively, come on strong with the flirting, or ask him out while he's still bruised from a breakup. I can tell you from experience that a guy who's just gotten out of a relationship, needs support and friendship. Then if it's meant to be betwen you two, it will naturally deepen into something romantic. Hope that helps you!