1. A curious mind. I get suspicious if the person I'm interviewing doesn't ask any questions. Our most recent hire, when he interviewed, asked me about our strategies, wanted to see a strategy, asked about the worst part of my job, wanted to know about the structure of the place, the process. He asked me about our client relationships. He asked me what was my favorite work out there. He talked about the kinds of classes he likes to take and his philosophy of always trying new things once. It said he was interested in growing and learning as much as he could.
2. Drive. I like to know that the person has had to work really hard at something. Maybe there's a project that the client killed but they executed anyway because they loved it. Or a side project. Maybe they run a successful website or have started a business or invented an app. Maybe they run marathons or wrote and directed a full-length film. All of those things tell me that this person has the will power to accomplish things.
3. Enthusiasm. Some people are more low-key than others, but occasionally I'll have someone sitting in my office for an interview and I'll want to reach over the table and feel their neck for a pulse. Creative businesses run on the energy of the people. You don't have to be loopy, but it's nice to, as my little league baseball coach used to shout at the outfielders, "look alive."