Hello. Your first day of work is very important since that will create an impressions from your boss and even workmates. First thing, be punctual. That will speak a lot about you if you come on time. Also, maybe what you can do is just to stay calm. Be positive that all is going to turn out well. Try to be friendly if you can so that people will see you as a good person to work with. With your boss maybe you can show him how interested you are to start and learn more about your job. You can be very honest in asking or clarifying things that are not so clear to you or even in doing things you are not so sure of. Remember, always ask when in doubt. That would be better rather than pretending that you can do it when in fact you are not sure how to do it. That would be more dangerous. Finally, consider your first day at work as a new day that you can be productive as a professional and be eager to look forward to days to come. Good luck!