She has to be "friend" material. If I couldn't be "just friends" with her, then I'm never very confident about a dating relationship. By "friend" material, I mean nice, friendly, interesting, intelligent, funny (this is a big plus for me).
As far as looks. I'm not too picky. Cute face, cute figure (very obviously female, but no "baby got back" for me), and most importantly, a nice smile that shows itself frequently. If she doesn't look like she's enjoying life, I'm probably not going to enjoy being around her (I'm a very smiley person as well).