I have interviewed many, many people over the years for positions from entry level hourly to director level; let me share some tips for you job searchers.
1) Do your research. I can't stress this enough. One of my favorite answers to "what do you know about our company?" : "I don't even know who you are" This after we had been speaking for 2 minutes and I had fully identified myself and my company.
2) Be consistent. It is likely that you will interview with more than one person. Do not make the mistake of thinking that the first person who interviewed you has no weight in the decision. I have had candidates who are cavalier, even rude with me and completely different with the next person in the cycle (all on the same day).
3) The person who called to screen you and the person at the front desk are your friends. They are also mine. I ask them how you treated them. If you treated them poorly, I'll know and I may not even interview you.
4) Be honest. We check.
5) Be prepared. Remember, you are interviewing us as a company as well. Ask questions such as, "Why did you come to work here?" and "Please tell me about the culture of the company" There is nothing wrong with asking about the financial health of the company--unless it is a public company, in which case see item #1.
6) Be enthusiastic-even if this is your 4th interview today and your seventeenth month out of work.
7) NEVER, ever tell any interviewer that you are just interviewing "for practice", even if it's true (I do recommend interviewing a lot). It is insulting and a waste of our time. You may not be looking for work now, but things change and people move around a lot. I'll remember you telling me that if we meet across a desk again some day. On the other hand, if you call and ASK me if I will interview you for practice, I'll make the time. It's also called an informational interview and some of us love to do them.