Job Interview at a natural health store?

I am 16 years old and interested in herbs, massage/aromatherapy, and natural/alternative health. I am a vegan and super knowledgeable about health food. I applied at a local store that stocks herbs, vitamins, supplements, organic foods, and does massage – they actually gave me an interview!

So, what should I wear and should I study up on anything that they may ask?
Anything important to know about any job interview? This is my first one.
Anyone with experience in this field would be awesome. Thank you!