Women are attracted to confidence, so just act confident and ask her out. And don't wait too long, or you will end up in the Friend Zone.
Next time you talk to her, mention some restaurant or movie that you're interested in. If she is interested in you, she may express interest in the restaurant or movie that you mentioned, giving you the shot to ask her out. But if she doesn't make it that easy, ask her out anyway. The worst that can happen is that she is still flattered, but maybe decides that you two can't be friends. And that wouldn't be a loss, because you can't really be friends with her if you're attracted to her.
Good decisions come from experience. Experience comes from bad decisions.