There really isn't an exact answer to this. But my answer to it is to get her attention and ask her out. If she says yes, good for you. If not, don't give up and try to get to know her a bit more....
First figure out why. There has to be a reason. Then you have to show her that you do. Tell her how much she means to you. Us girls tend to find that guys lie about most things. you have to prove to...