First impressions matter. If appropriate, ask ahead of time about what to wear. The safe bet is to dress professionally, paying attention to grooming, colors, and accessories.
If you are a coffee drinker or smoker, or you have lunch/breakfast before an interview, use a mint or brush your teeth before starting.
Also, remember do not chew gum, be conscious of how much perfume/cologne you wear and remember to exude confidence - head high, stand straight and tall, hold a slight smile, and relax.