As a rule of thumb, dressing in a suit for an interview wouldn't do you any harm. You must be able to capture the tailored look, but in a feminine manner. Double breasted in navy or black, perhaps softened with a scarf rolled under the collar, its a classic which will never be out of style.

A good idea is to find some information regarding what other people in the office wear. If you think a suit will be too formal, maybe you could consider wearing a pants suit or just a good blazer and skirt. You may also consider to wear a coatdress because it is very tailored, but a little less formal than a suit. If, on the other hand, the place is very conservative, and they all wear dark suits all the time unless they are at a picnic, brown instead of gray could be a wrong choice.

Shoes are very important. They don't have to be trendy, just the best that you can afford and carefully polished. If you don't own a decent bag to match, take one and just hide it behind your briefcase or portfolio.

Hair style is important too. A pony tail is always nice if you have a good face for it - with a beautiful barrette.

Use a nice makeup. Be sure your foundation matches your face. Don't do anything that would cause one part of your face to stand out more.

Wear a little something that makes all of the above you. Whether it's a great lilac-colored shirt because the color's so flattering on you, or grandma's heirloom earrings.