Ask her in casual conversation if she has boyfriend.
If she says yes, unless she just likes having someone around (which is a bad sign), your chances are slim.
I suggest you quit.
Talk to her, see if she is interested in you. How will you know?
If she stands close to you, smiles at your jokes, looks you straight in the eye all the time,
touches your clothes, asks your sign (in horoscope)...
How to ask her?
Do it yourself. :)
Really. You are not the first or the last. Think of what you will say go to her and ask her.
If during conversation it seem it might not happen, quit.
If you ase her, and she says no, don't worry about it. Consider it a practice :) .
Besides, someday some girl might ask you out, and you might have to say no.
It is not that bad, and it is nothing personal.
Do not send someone else to do it for you. She will see it as you are not interested enough to ask her yourself.
Or, you do not value her enough, to make an effort.
Besides, most girls want someone to ask them out. Perhaps not by you, though ... :)
Remember this: girls are just as insecure as boys are. Even more. :)
Hardly any women is satisfied with her body. Weird huh? :)