There's a lot to say about this actually.
1) A social life is a must -- some kind of social interaction with people... anything. Even if you're a part of some small-end/not very popularized club on campus, it's something that displays some sort of social value. Fact is, all PUA theory and practice aside, if you're not actually out there, meeting people and interacting with people... how do you expect to even meet a girl who'll entertain the idea of being your girlfriend?
Name of the game at this point is displaying social value.
2) Once you have a social life or circle you're apart of -- it's about leadership (or what PUA call being "alpha"). You don't need to be captain of the rugby team or dance squad (hey man, what ever you're into). Women are genetically hardwired to find the "alpha" or the "leader of the pack". Why? Because to their cave-women genetically programmed side they're always going to look for the strongest one who can take care of them and provide for them. So if you're the social outcast and not a "leader", you're displaying qualities that are unattractive. No girl really goes for the outcast (aka the sick gazelle at the outskirts of the heard).
Listen, there's nothing wrong with being a strong introvert who's independent and likes doing your own thing. That's actually really great! I'm the same way. Women love that in men. The difference is that you want to be the kind of guy people will want to follow. Be the guy who makes the plans with your friends, be the guy who people want to do whatever you're doing. Most importantly, be consistent with your decisions. If people don't want to do your plans, that's ok! Still say "alright, I'm doing it anyway" and actually follow through. Those are qualities that exemplify the leadership aspects that women love.
In short, have a social life and being the leader of your social circle. Be the guy everyone wants to be around, but not the guy who needs people to validate who he is.
You could troll this forum and learn all these techniques and strategies to pick up girls and bring them into your life, but I think you'll find that you're going to only attract certain types of women. Practicing what I said and you will see that interesting, genuine, and positive women will be drawn into your life with no manipulation. Aka, women you'll actually want to have around for a long time.
I'll also add, that in my case, I built my social circle from scratch. It takes time, there's no quick "here's how to get a girlfriend" (that's worth while at least).
Hope this helps (and sorry if it seems preachy, I know other people will read this as well),