Stay calm and ready to listen. Try not to gesture too much or fiddle with your pen in case you annoy or distract your interviewer. Sit upright and comfortably in your chair and maintain good eye contact. Remember to breathe effectively as this will help you feel less nervous!
If you are offered a cup of tea of coffee, feel free to accept one. However, keep in mind that if you are nevous, you might spill your drink and a biscuit can easily crumble onto your clothes. If you want a drink, a glass of water might be best.