tips: be your self , be honest, talk about the thing you enjoy doing and any passions you have if asked.
not every job needs a wealth of experience. Try not to be too nervous if you are that doesn't matter either most people will be nervous.
take time while your there to consider if this is a company you want to work for can u get along with the staff ect, its all well and good getting a job but nobody wants to be stuck with people they don't like.
clothing- Just dress sensibly the jobs i interview for need safety equipment so its slightly different for me, wear some thing comfortable but not too extravagant black shoes if you have them.
as for the last question i am unsure, on the day before the interview i would think to my self if i was a customer here what would make my shopping experience more enjoyable/ relaxing