wear something thats not like.. a suit and tie or something
i'm going to assume your a girl? maybe dress in like.. a pair of nice jeans and a fitted shirt
don't get tooo dressed up for a store like that, if it were me.. I'd wear an outfit like what you would buy there
smile, be friendly, make eyecontact. don't say anything negative about yourself just be positive
and my biggeessttt tip because this for me always helps
ASK QUESTIONS!!
An employer is going to want someone that WANTS to learn and know more
at the end of the interview, he'll probably be like "so do you have any questions" even if the interview is pretty cut and dry.. be like "so how long have you worked here" or something like that, let them know that you are interested!
and most importantly..
don't ask about how much you are going to make... benifits (if any) or stuff like that.. they don't want someone whos going to nag
and I do wish ya luck
let us know how it goes