Read. Then read more.
Of course you’ll do research on the company before your interview, but it shouldn’t stop there. Come prepared with what the company says about itself, what the industry says about them, what their competition is doing, and industry news and advances. The company you’re interviewing with is full of people that know what they do. That information alone will make you seem prepared, but not an asset. When you come to the interview looking and sounding like an expert in your field, it will take you much farther than just knowing a mission statement.