Asking out a guy that you like isn't always that simple. You have the fear, the nervousness, and the pressure. When you ask a guy out, you have to put all those things aside and do the following...

If you haven't already, get to know the person. Say "Hi" whenever you see them and find out about them. Also, let them get to know you.
Become friends with the person. It is a lot easier to have a crush on a friend than on a stranger. Get to know their interests and who they hand around with. (boys, girls, geeks, preps)
Look for signs like staring, trying to get your attention, talking about you, and touching you. If a guy likes you, he WILL find a way to touch you.
Make your move. Talk to him about a subject on relationships such as his status(is he single?), dating spots, and free time.
Ask him if wants to do something on a certain night. If he answers yes quickly, he really likes you and has liked you. If he says he has to check his calendar, tell him never mind. If he really wants to go out with you, he will say something like, "No, wait, how about Saturday?"
Ask yourself after the date...
Did he seem like he enjoyed himself?
Did he kiss you during or after the date?
Did he give you his number? (his correct number!)