You have done all of these things, in part, to put yourself at ease. You know that the less you have to worry about ("Did I shine my shoes?"), the better your performance will be.
There is, however, at least one other person you should seek to relax: the interviewer.
You may think, "Why should I worry about that? The interviewer has the power, and I don't." That is precisely why you should strive to make that powerful person feel comfortable, even happy, in your presence. A great many interviewers hate interviewing. They know they're not good at it, and they are dealing with strangers and asking questions to fill a job with which they are unfamiliar.
So what should you do? Be friendly. Pay attention to eye contact. Listen carefully to what is said and, if a question is unclear, seek clarification by rewording it. (Don't do that too frequently or you'll sound like a parrot!) If some glitch arises, laugh it off. Be wary of challenging a question unless it is patently offensive. Stress your ability to work with others, and then behave like a person who can do so. Let your body language signal that you are both professional and amiable. Don't ask any questions that might put the interviewer on the defensive.
If this seems like the behavior of a sales representative, you are right on target. Good salespeople make their customers comfortable.
Michael Wade writes Execupundit.com, an eclectic combination of management advice, observations, and links. A partner with the Phoenix firm of Sanders Wade Rodarte Consulting Inc., he has advised private and public-sector organizations for more than 30 years.