look smart, smile and introduce yourself, and shake hands.
Take your folder, it shows you are really interested and they can read a little about you. Do you have a CV/Resume? If you do take that too. Provide referees such as your school, or personal referees.
Find out all you can about their shop. Do they have a website? Find out how long the business is running and future plans Do your research, it shows interest and commitment.
Ask them questions too. About the shop, and the job.
Remember to be yourself, dont be over-confident though, but do show that you are geniunely interested in working for their shop.
Hard to say much else without knowing what kind of shop it is, but anyway, best of luck. The fact you are asking questions about it shows you are interested and thats halfway there already!
Fingers crossed for you! x