This is one of those posts that makes me worry I'm going to come off as some cranky old coot. But I still think it's good advice.
If you're interviewing with an agency, and the person asks you what you're looking for, as in like a job, or what you're seeking in life, that's really another way of asking "why do you want to come work at our agency?" So please don't let your first answer be, "I really want to live in California."
That may be true. California has its perks. But there are 1400 ad agencies in California. There are 26,000 creative companies. And there are 12.2 million available jobs, not including couch surfing. So answering that you want to move to California, while it's a fine lifestyle choice, isn't what your interviewer wants to hear. It's one step above a shrug and a mumbled "Dunno."
Maybe say something work related, for starters. You're looking to go to a place that does amazing creative? You want to learn and grow? You just want to make cool shit? That at least narrows it down a little. It implies something about the why you and the agency you're talking to are a good match beyond its physical location.