In my opinion, you can never go wrong with wearing a basic black suit to an interview. If you're a working girl, and by working girl I don't mean hooker, you need a properly fitted suit in your closet. A suit consists of a blazer, dress pants and/or a pencil skirt. In my opinion, you should have both.
Any interview outfit should be topped off with the right accessories. Personally, I always wear heels to interviews. If you do wear heels, basic pumps are the way to go. Leave your stripper shoes at home. Simple jewelry is fine. Just remember that you don't want to wear anything too distracting. You are there to obtain a job not walk the runway.
blazer // skirt // top // pumps // bag // necklace
Another interview outfit that's both simple and classic is a well fitted sheath dress and a pair of nude pumps. Dresses and skirts should be no more than a couple inches above the knee. Your boobs shouldn't be on display either. Covering the girls up is Interview Etiquette 101.
dress // pumps // bag // necklace
Last but not least, if dresses and skirts aren't your thing, a blue blouse, dress pants and patent pumps can go a long way. According to various studies, blue is a great color for interviews because the wearer exudes confidence. According to a lot of the same studies, red is a bad color to wear because it evokes too many emotions.
top // pants // pumps // bag // earrings // ring
Regardless of what you wear, remember one thing: