Well, this just actually happened to me today so I might as well share.

I've been dating this girl for a few weeks now and we normally party together and after a party I was walking her out to her car and I could tell she was digging me and so I swooped in and kissed her and started to walk away. She grabbed my jacket and we started to make out. I only saw her once after that (excluding today) and she had to go abruptly and that's understandable. Today she came to watch me play my basketball game and as I was walking her to her car I kissed her once and asked, "You just wanna make this official now... ya know, boyfriend and girlfriend?" and she said yeah. So, there ya go. Come to think of it, I've used this approach on every girl I've dated.. weird.