Learn about the history of the company as many people tend to go there with no knowledge of the company and this will make you seem like you don't care.
Do your research beforehand about the company and why jewellery is important. You will be asked to roleplay in the interview where you'll have to try and sell a product to the interviewer, but it's really not that bad.
Dress smartly and be pleasant.
Also, this doesn't always happen but it did with me:
I arrived 15 minutes early for my interview and was left on the shop floor to look around for 15 minutes. I chatted to the girls who were working before being called in. Later found out my manager purposefully made me wait on the shop floor to see how I interacted with the other employees. Not every employer will do this, but always make an effort with the employees that already work there. You can bet the employer will ask them what they thought of you once you left.