Help for job interview!!?

Im 16 and have an audition today for a small jewellery company near mine. It has a large website and two shops in my city (leeds, england). It sells some expensive and high cl jewellery and they seem interested in me. I have worked in a top star hotel as a waitress but i feel this is not for me anymore and i dont enjoy it. I want to show them i can work for them and i am mature and friendly and easy going. Any tips would be great. Also what type of questions would they ask and what should i have prepared? I do have ideas and stuff written down but i really want this, thanks.