The most important thing to do before going into an interview is to try to relax. We’re going to set up a relaxing “space” now, before the interview, so you can use it during the interview. Take a breath. Seriously, right now, as you read this, take a deep breath. Breathing is a way to calm yourself, move your chattering thoughts into the grounding influence of your body, and exist in the present moment. The more you can get into the habit of taking a deep, conscious breath, the more your body will connect it with slowing down and relaxing. Practicing a deep breath in a safe, calm environment will help you access those same calming feelings when you repeat the breath during your interview. It can be helpful to think a soothing phrase, like, "It’s OK.", "You’re fine.", or, "You can do this." (Keep the phrase short, positive and silent!).
As you think about and prepare for your interview, continue to practice the breathing technique. When you get stressed about what’s might go wrong, take a breath, "It’s OK." When you remember things that went wrong in past interviews, take a breath, calm yourself, and then figure out the lesson of that situation.
Your future employer expects you to breathe, so this calming technique is something you can use during the interview. As you walk into the interview room, take a breath. If you have a break during the interview, remember to take a breath. Tell yourself, "You can do this." Of course you can.