Really know the language that the company you are interviewing for uses. Don't think you can pull it out of your ass cause you worked in it 3 years ago. Languages change a lot. I don't have time to teach you how to deal with Exceptions in PHP 5, because frankly you aren't worth it if you can't do some homework before you come in for an interview. This goes doubly so if the posting says "PHP Developer" right in the title.
I know we're your fifth interview this week, and frankly I don't care. I get 60 minutes to evaluate whether to give you commit access to my code, code I've spent the last year preening over and perfecting. Separately, I have to evaluate whether I want to be stuck in a room with you for 8 hours a day, potentially for the next several years. You better be on your best behavior, and you better want it, and you better be excited, because if you come in here looking like you're just looking for something to do or a buck to make, you're going right back out the door. But if you want to create, if you want to make something beautiful, you'll be on my short list of favorite people, people on whom I'm going to tell my boss to spend a lot of money.
Have a passion that isn't code. It's not a dealbreaker if you don't, but I really like to see people with multi-disciplined lives. Back when you applied for college, there was a box labeled "Extracurricular activities". If you left that box empty back then, you should try and fill it soon, because it's there for a reason. Musicians write more interesting code. They see patterns I don't. Foodies know where all the good restaurants are. Gamers bring in their xboxes. Diversity in a small office is vital, because we're all going to spend more time here than at home, and if all we do is our jobs, we're going to run out of things to talk about real fast.