I suspect a lot of my readers know this already, but here's a good short guide to talking to the press, written from the interviewee's point of view.
The only thing I would add: if you don't have anything to say, don't say anything. If you're initiating the conversation, make sure what you have to say is really newsworthy, and be prepared to explain why. If I'm requesting an interview, make sure you're prepared to have a substantive conversation about the topic. A content-free or off-topic interview doesn't do either of us any good.