The general rule of thumb in a corporate setting is dress for your boss's job. Good grooming is essential. Wear a neat hair style and avoid extremes of hair color, nails, jewelry or makeup. Shine your shoes, press your shirt or blouse and take a good long look in the mirror. Just as your resume is your advertisement, the interview is your sales-pitch.
Enthusiasm goes a long way.
When asked about a previous employer, even if your experience there was not the best, put a positive spin on things. Be honest and forthright, but not self-deprecating in your answers. And never, never lie. The consequences of being found out far outweigh any possible benefit you may obtain from a stretch of the truth. While the company representatives are learning about you, sizing you up against their needs and corporate culture, you should be doing the same things.