Rule # 1: Don't go trying to make a specific girl your girlfriend. If she doesn't dig you in that way, you're gonna be hard pressed trying to help her become interested in you in that way. It probably won't work and you'll be so focused on that doomed to fail goal that you'll miss several other valid opportunities.
Instead, just choose among those women who seem interested. What's that? No women are interested?
Rule #2: Be somebody who women would want to date. Oh great, "be attractive" in other words, right? Well, some aspects it's different strokes for different folks. I've got a forehead you could land a plane on. So if girl A thinks that a thick head of hair is her jam and it's super important, then that's a different folks situation for me. I'm gonna have to look elsewhere. But there are some implementable strokes that a whole lotta folks seem to agree on:
Work out, take care of your body.
Be presentable. Clean your room/house/car, your clothes should smell fresh and be somewhat wrinkle free. Have manners when you eat.
Be passionate about something.
Rule #3: Be where women are. You don't have to sacrifice all of your dudes-only hobbies, but you shouldn't complain that you never meet women if you aren't doing things that women also enjoy doing. (And the fact that there is a girl at your Magic the Gathering fest doesn't count, remember Rule #1.) You should choose things that you also enjoy. You legitimately having fun is an attractive thing. Conversely, you showing up at an event you've got no interest in just so you can creep on all the women there is an unappealing thing.
Rule #4: If you sense that she might be interested, ask her out. (Don't waste any time trying to increase your "yes" likelihood by trying to do baller shit in front of her first. Remember Rule #1.) Be very open with your intentions. This takes balls. She might say no. Even if she says no, be proud of yourself that you had the balls to ask (and respect her no - remember Rule #1).