Just be courteous and pleasant. Say her name out loud, scientifically proven to raise her awareness of you both in the obvious way and a romantic way. Be relaxed, It can be nerve racking being around the person you like, but by being more relaxed and comfortable you create a more comfortable environment for the other person, which can open those communication channels :)
approach her, ask her hows she's doing than compliment her (a nice compliment) not "your boobs look nice, as much as guys think telling a girl she had nice boobs or a nice ass is a compliment, its not! unless she has no self esteem or you two are already dating. compliment her smile, her eyes, her hair, compliment her on the colors that she's wearing and then ask her "is it okay to keep her company for a bit" just in case she wants you to go away and i think that should be okay as long as you can keep the conversation going then ask her if you can take her out to a lovely place of her choice.