For me it boils down to being a kind human being with passions I can relate to!
Shared nerdy interests and a willingness to have silly or insightful discussions about them are important to me; not only do I want to be able to spend time with someone doing something I'd enjoy anyway, but I also want to be able to reminisce and geek out about these things when we're just chatting. It comes down to me wanting to be able to be friends with someone as a foundation to the relationship.
A willingness to communicate and an open mind are vitally important to me. My life partner has spoiled me in this regard; they don't beat around the bush or play mind games, and it's that honesty that allows us to go through our relationship without the fear of tiptoeing around one another. This isn't the same as being inconsiderate of each other's feelings; it's about trusting one another with our feelings, whatever they may be.
I like people who have a passion or ambition they work toward. I want to be able to cheer someone on and for them to ramble about something that might go over my head at first. People who can teach me something new through their enthusiastic example give me joy when they show that enthusiasm to me, especially because I really feel like I am joining them in their adventure through life! (What can I say, I love a good story!)
Appearance does matter to me to a certain degree; my tastes tend away from the "sorority girl" look and much more toward the "subversive queer" look, likely because my best friends though my life fall among the latter. Apart from that, good hygiene is important as hell, and a genuine smile is really attractive.
Finally, people who treat service workers with kindness and respect are sexy as hell