It's different for different people. For many it's looks, for some it's personality, for others it's intellect. I'd say for most though it's some combination of the three. I'm attracted to someone who has a kind personality, is reasonably smart, and is somewhat attractive. Another important factor is similar interests, in fact I'd say that's one of the most important things. Common interests are a great way to help get to know other people and to help people get closer.