During the interview process is isn't all about just what you say and how you answer questions. There is an unspoken criteria that revolves around how you carry and present yourself... it's your job interview etiquette.
Your business mannerisms can many times be the key decision point for interviews when the short list of candidates are so closely matched for any given position.
For example, you must be someone who is comfortable maintaining eye contact throughout the interview process.
During the question and answer process, it is certainly acceptable to break eye contact and glance away while you are gather your thoughts. But the inverse is not so true. If the interview is speaking to you, then you want to maintain eye contact with them and completely focus... even if the interviewer doesn't maintain constant eye contact.
This not only sends the message that your are completely focused on the task at hand, but it is also the respectful and polite posture to assume.
During the interview, under no circumstance should you be chewing gum or even sucking on a mint. If you want to freshen your breath before the interview, get that done ahead of time. Don't even greet the receptionist with anything in your mouth.
Whether you agree with this being rude or not... it is, at the very least, distracting.
Make it a mental point to remember your interviewer's name after you are first introduced to them. Then use conversationally as you would anyone's name... just don't over do it.
In fact, if the company contact person tells you the name of the person who will be interviewing you, then by all means, when you greet them, call them by name.
And by all means, personally thank them by name for their time at the conclusion of the interview.
Manners, etiquette, and class go a long way in getting yourself remembered as part of your interview and this might just be the edge you need when all other factors with your competition are too close to call.