You guys need to do things in the proper order. As soon as you realize that you are attracted to a woman, approach her and flirt with her. Then ask her for her number. Call her up, or text her, and ask her out on a date.
What doesn't work is to become fake-friends with her in hopes that the friendship will turn into something more. You will quickly get stuck in the Friend Zone and writhe in pain while she dates more assertive guys who just asked her out.
Good decisions come from experience. Experience comes from bad decisions.