A few tips that have served me well over the years:
1. Keep reminding yourself that the worst possible outcome is that you won't be offered the job. It won't be the end of the world, and there will always be other interviews and other jobs. This helps put one at ease. However much you may want the position, your life does not depend on it, and in the event of failure, you will move on.
2. Do your research about the company and the role. Interviewers dislike candidates that come in on that day clueless about the position and what it entails.
3. Be proactive, and don't just wait for their questions, hoping that you would be able to keep them at bay. Interviewers will chew you alive in that scenario. Take the initiative, ask questions, and very subtly, put them on the backfoot. By the end of it, they should be selling the position to you, rather than judging if you are good enough for them.
4. Always leave them wanting more. If they ask a question, answer in a way that piques their interest, and they are forced to ask follow-up questions. This allows you to steer the conversation in the direction you want. There is a fine line to tread here, because you don't want your answers to be so short and straightforward that they move on to the next question on their list. Instead, it should be just right in terms of detail, and there's something in your answer that forces them to dig deeper.