At first, I have to either think she's cute, or she needs to do something to be noticed such as be funny or act nicely towards me.
To get past the initial notice, she needs to demonstrate intelligence but with warmth. She needs to show passion and imagination, but tempered with responsibility. I look for empathy, honesty, and a self-confidence which can still be transparent and vulnerable. Above all, no whining or being critical about others (at least until we know each other *really* well).
I've only found one woman who meets all those criteria, so I married her.