I'm advising this with the assumption that you are female.
Make sure you do not fidget, such as playing with your hair. It's a distraction to the interviewers and they may focus less on what you are saying and more on what you are doing. Get your point across without rambling and make sure you keep it slow, in order for them to understand you. I talk very fast when I'm nervous and it is a big red flag that you are not confident with what you are saying.
Breathe normally, relax and realize that they're people to. Even if you DO show that you're nervous, they understand it is a stressful situation. Just answer the questions honestly. You don't need to practice the truth.