To make a good impression that you are a capable employee and are a serious candidate wear professional business attire.
For men this means a suit (navy, grey or black), long sleeve dress shirt (white or a color that matches the suit), belt, tie, dark socks, dress shoes, minimal jewelry, along with a briefcase.
Hygiene is important so be sure to have a clean hairstyle, and shaven. It is also important to keep your nails trimmed as well.
Women interview attire is a suit (black, dark grey, or navy), suit skirt (appropriate length so that you can sit without worrying), matching blouse, shoes, limited amount of jewelry (should not be distracting the interviewer), appropriate hairstyle, neutral pantyhose, light make-up and perfume, and a portfolio or briefcase.