Show some initiative.
Do not wait for the other party to make the first step. Maybe she is waiting for you.
If she is interested, you will see the signs. If you ask her out and she is not interested, that is ok too. She will probably be flattered.
But, if possible first check if she returns the invitation. (The smile, or looking at each other slightly longer then it is usual.)
Accidental brush of your bodies together, touching your shoulder, removing loose hair from your clothes,
standing close, looking at you longer than usual, asking personal questions, smiling at you jokes.
Just look into her eyes. You'll feel the connection. Or make one :), perhaps.
Anyway, it is better than staring at her breasts. Not to mention it's rude. To stare.
Ask her out/on a drink, or ask her personal questions, return the stare, smile.
Do not worry about the outcome, asking someone out usually lifts other people's self-confidence.
It's OK to be nervous about it. Breathe deeply and you'll feel better.
Maybe you imagine girls to be perfect. They are not, unfortunately. They are humans, like most of us.
Girls can be lost just as lost as we are. Sometimes they are scared, nervous, insecure or clumsy. :)
Sometimes you win with girls, sometimes you don't.
Sometimes we are scared or insecure.
And, in time, you will be in a person being asked out. :). Even if you say no, it is not so bad.