For me, it doesn't usually matter how they look, it's how they carry out a conversation. Like if I overhear someone saying something seemingly intelligent/witty, I will immediately fall for them and try to get to know them better.
Most Helpful Girl
Listening to them being passionate about something they really enjoy. And seeing how it makes them happy and how talking about it kinda just lights up their face.. yeah. Usually makes me get all soft-hearted and melty towards them.1