I'd say the first is always the obvious physical appearance. I mean, it could be something I'd get over later, I guess, but "Hmm, she's pretty hot" is generally my first thoughts upon seeing a female, primal thinking or not. That said, though, my standards have gotten different as I've gotten older, so it's more complex than just "lol she's got big boobs!" or something as far as physical attraction goes. On the same point, too, if a woman looks good, to me it's a good sign in some ways, as it generally means she has the self discipline to eat correctly or exercise, so her values would not clash with mine. But, at the same time, I'm smart enough to know just that a girl being hot doesn't make me and her able to actually have a relationship, so while it initially attracts me because I have eyes, you know, yeah...
Besides that, religious views is a deal breaker for me. A girl I'd actually date, has to be Christian, and actually act like God exists. That's a strict requirement.
Once that requirement is fulfilled, well then, not so much her knowledge or whatever, but I want a girl who's not afraid to think. Like I don't care how much base knowledge she comes with, like, "out of the box" but just as long as she's willing to learn and try new things. I don't care how smart she is, per se, but I don't want a girl that'll shun knowledge and learning. On the same point, too, I don't want a girl who's a pseudo-intellectual snob.
Girls tend to be stupidly picky with guys, so I'm being picky with girls back. So I don't complain, as I realize I could "get with" lots of girls, but most girls don't fit my requirements, so I don't bother. That, and it seems like "fixing" a girl is a futile proposition, as girls do it to guys and it never really works. Some girls apparently think of guys in the same way I think of project cars.