Following up.  Following up after an interview is a great idea.  It keeps you freshly in the mind of the interviewer, shows you are interested and indicates that you are proactive.  One follow up is great.  More is questionable to me, but might be OK to do others according to the industry. For example, in sales, tenacity can be of great value. But for most other positions, more than two is going to possibly draw the ire of the interviewer.

Business vs. technology.  Most employers these days are looking for candidates who can provide value.  This may be value to customers, value to the organization, value to end users, etc.  Most interviewers will give you the opportunity to add comments about items they haven’t asked about.  If they don’t ask you about how you have provided a business value to your organization then this is a great opportunity to do so.  Remember, reducing total cost of ownership is only one way to create value.  The ability to increase an organizations return on investment, which may cost the organization more on a technology level, can often end up increasing revenue or…

Stay on topic.  Remember that time is something many do not have.  When you get off topic it can cause interviews to take much longer without filling in the blanks the interviewer is looking to fill in.  Most of us have a set of requirements we need to verify a candidate must fulfill.  This is difficult when the candidate strays across topics.

An offer isn’t always a final offer.  Feel free to negotiate during the interview process to get what you want.  Hopefully each position is looked at from a long-term perspective.  Set the foundation early and if the organization isn’t willing to meet your needs then perhaps the position is not a good fit.

Confidence is confidence inspiring.  Be confident in an interview but not cocky.

During your interview make sure to ask questions.  These can be about the job at hand, etc.  But don’t phrase the questions as demands.

If you are interviewing for a job then research the company first.  Know what you can about the history, structure and mission and point out places where there is synergy between you and the company.

Always have a copy of your resume with you.  Some interviewers ask for it just to test you…

Make sure to keep eye contact with whomever you are interviewing with.