When you are waiting to be called into your interview, calm your breathing and relax your shoulders. When we are nervous, our voices dry-up, so sip some water before you start the interview. This will also help ground you and bring you into the present moment. At the start of the interview remember to shake hands (if face-to-face), smile, make eye contact and then sit up straight.
Pay attention to your body language before and during the interview - our body language influences how we think and feel about ourselves, which in turn changes our behaviour and changes our outcomes. It’s a little bit of “fake it until you make it”, which research by Amy Cuddy shows is more like “fake it until you become it”.