My 2p worth (as someone who has been on both sides of the interview table)
* the most important factor is how you perform (answer) at interview. Your application got you into the room now sell yourself, dress code is secondary but be clean, neat and tidy.
* do some research - is it a local company or a chain? What is the normal dress code of the staff (Company Tees or polos? Ties? - this should help you judge what to wear at interview but at least have a 'quiet' tie)
* Check what brands they sell etc so you can plan some questions for them.
* Prepare a few answers to standard questions - you'll be nervous so having a few answers prepared will help. Write them down and take the paper with you. Take notes during interview if you want - they will take notes.
* They may ask about: why you want the job, experience, what are your strengths and weaknesses, what good things you've done in past (and bad). Make sure you answer with more than a YES/NO.
Good luck.