I find it helpful to remember that interviewers are often as nervous as the people they're interviewing. I've had to interview people, and it shows you another side of things. Think of it as meeting a new person and having a discussion about business.

It's a good idea to try to make the interview a DISCUSSION (a polite and professional discussion), rather than a question-answer session. It's easy to think of it like you're being quizzed; unfortunately a lot of places set the interview up exactly like that. But having a discussion is something everyone is good at. Ask questions of your own when they come to mind. Ask about the company. Ask what it's like to work there. Ask for the interviewer's opinions of things.

Remember that an interview isn't just to convince a company to hire you, it's for a company to convince you that you should accept the job. Try to learn enough about the company so you can tell if you want to work there.

Also, be yourself and be honest. Don't pretend to be a brainless optimism machine. No one is and it looks fake. Better to be calm, confident and honest than to sound like a liar.