My confidence, knowing a little backstory about the employer, and being curious to learn more from the employer during the interview. That keeps me calm, because I always go in with an open mind and no expectations. Expectations always make people nervous in interviews because they can be desperate because they really need a job at the moment, other stress in their lives they’re battling at the moment, etc. Remember always to go in with no expectations, but remain confident and positive; it will show in your body language and your tonality.