What you wear to the interview depends on the job you're applying to, so do some research on the company dress code. However, a good rule of thumb is that it's better to be overdressed than underdressed. For example, even if a company has a very casual dress code where t-shirts and jeans are allowed, it's best to wear a collared shirt. This shows that you're serious about the position and made an effort to look your best.
How conservative the company culture is will also affect what's appropriate to wear in the office, but it's better to err on the side of caution. Keep your hairstyle neat. Men with long hair should pull it into a ponytail or even consider cutting it. Bright coloured hair dyes should also be avoided. Cover up tattoos and wear simple or no jewellery. Wear clothes in neutral colours, nothing too flashy. Unless you're in the fashion industry, you want to be remembered for your qualifications, not your unique outfit.
Choose shoes conservatively, some that you know you're comfortable wearing. You don't want to buy new shoes only to find out they squeak on hard floors or pinch your toes unbearably after wearing them for thirty minutes. Closed toed are the best choice; never wear flip flops. Women should wear flats or very low heels if you're comfortable with them; no stilettos!
Once you've chosen your outfit or narrowed it down to a couple of choices, try to do a practise interview with a friend or family member while wearing it. See how comfortable you feel in the outfit and ask others' opinions on it. Does it fit well or does something itch or keep riding up? If you feel the urge to be constantly adjusting or fidgeting with some part of your outfit during practice, you may want to change it. Wear something that makes you feel comfortable and confident!
Research the company dress code
Make conservative choices
Wear comfortable shoes
Practise in your outfit