Sort out your clothes the night before. Make sure you have an outfit that is smart and presentable. For men, it doesn't have to be a suit, but a shirt and tie is still the norm. As for women, any company that expects you to wear a skirt or dress is hopelessly out-dated. So you should feel perfectly at ease in a trouser suit or similar if that is your preferred outfit. As long as you appear smart and well presented you should be fine. Avoid casual clothes and make sure that everything that should be buttoned is buttoned.