6. Dress well

The interviewer is dedicating his or her time for this interview, and he/she would expect the candidate to give the interview at least an equal weight. A well-dressed candidate leaves an excellent impression and projects the image that he or she really cares about this interview.
This rule applies even if you are interviewing for a company known for its casual dress policies (such as many of the internet companies). Even in such cases, dressing up cannot go wrong. I have never heard any recruiter complaining that a candidate dresses too formally for an interview. However, many a candidate has been hurt by not properly dressed for the interview.