If she's into videogames I personally find that kinda sexy, but only because I'm a gamer and rarely find girls who are hardcore into them like me. As for details, if she's about the same height, doesn't dress to impress (heck, T-shirt and jeans looks sexy to me) and if she's got cute feet, flipflops (personal thing there)
If she's sweet and caring in behavior but can also have those weird crazy moments that make you go "Something is wrong with you" in a joking manner...bout does it for me :D
i like it when a girl can look plain when she wants to, but can also change into a completely different person when she does herself up, hair and makeup and all. I don't know why, just the ability to turn your "sexiness" on and off at will simply by dressing down or whatever to me says maturity and I like that.