Something that has helped me is having my family or friends interview me. Just be sure to breathe. Dress professionally and if you need to prepare write stuff down and study that.

I recommend practicing as much as you can. To calm jitters, you can look up some typical questions a prospective teacher can be asked during the interview and think about your response to each question. It can also be beneficial to ask another person to act as the interviewer and ask the questions to you as a mock interview. Sometimes, I get the jitters when I start to respond and feel I've thought of a better answer halfway through. Before you respond to the question, I find it super helpful to take a moment and think about how I would like to word my response.

Most employers know how nerve racking an interview is and will most of the time be understanding if certain things happen that are caused by jitters. But, you can always calm these jitters by reviewing and writing down answers to popular questions that these employers would have. Practicing an interview with someone else is another way to get more comfortable with an interview.