What makes women feel the “spark” aside from looks?

I’ve been single for 4 1/2 years, and in that time every rejection I’ve gotten has basically boiled down to the woman in question not feeling the “spark” with me. I’m average-looking, introverted, with a good job and plenty of hobbies. I know tons of guys like me who are in happy relationships, and tons who have been single even longer than I have. Since I’ll never be model-handsome or a life-of-the-party type, what can I do to help facilitate the “spark” between me and a woman?