My last post was somewhat negative. I acknowledge that. I was annoyed. Let me make amends by posting some useful, positive information for those who find themselves on the other end of the interview table (or phone).

1. Google Live Search your interviewer. Most recruiters will tell you who will be performing your interview. If they don't venture the information, then ask for it - chances are if they know then they will tell you. Take that name and do some research. Get to know what your interviewer is most likely to be questioning you about. If they have written a book on security best practices, then there is a pretty good chance they will ask you questions about security. Do drop subtle hints that you read their weblog - most tech people like to hear that - just be sparing in it. You don't want to come off as a stalker.
2. Be honest about your skill level. Many interviewers will ask you how you rate yourself, so that they can judge just how delusional you are. Be honest here. If you claim to be a 10 out of 10 in a subject area, then you had better be an absolute expert. A 10 out of 10 is expected to know that subject inside and out, perhaps even teach the interviewer a thing or two. Don't be too humble though. Rating yourself as a 2 out of 10 is highly unlikely to get you into the interview room in the first place.
3. Don't interrupt. When the interviewer is speaking, never (and I mean NEVER) forcibly interrupt them. I have had many interviews where the candidate would inject words, statements, or questions while I was trying to guide the interview towards the next topic. Doing that does not impress the interviewer with your profound wisdom. What it does is send a clear message that you feel your thoughts are more important than the interviewer's... which is nothing but a fast track to bottom of the resume stack.
4. Speak clearly. No need to shout, but you should be certain that you speak confidently and with ample volume to be heard clearly. Avoid slang terms - especially cursing! Try to provide concise and accurate answers, with as few "umms" as possible. And for heavens sake, if you don't know the answer to a question, just say it rather than trying to BS your way through it.
5. Be prepared to ask questions about the employer's business and work environment. Even if you already know the answers (you did research the company's website beforehand, didn't you?). This shows an interest in the company and team.
6. Be prepared to answer strange, sometimes seemingly irrelevant questions during the interview. Good interviewers are not looking for right or wrong answers to every question - they are looking for clues about how you work your way through problems and how you are able to handle stressful situations. This is especially true in the Consulting industry, where your reaction to a crisis is often more visible and more important than the act of correcting the underlying problem itself.
7. Follow-up. If you already did a technical screening and are now in for the "big face to face" interview, chances are good that you missed at least one of the questions during the screening. You should note those questions during the initial interview, and research them before going to the main interview - especially if the interviewer is the same person. Let them know that you felt compelled to research the topic on your own time, and that you now have an answer for that missed question if they would like to hear it. Chances are they won't want to hear the answer, but they will take notice that you followed up and did your homework in between the interviews.
8. Be calm. It is normal to be nervous. Some folks even have obvious nervous twitches that come out in full color during something as stressful as an interview (sweating, fast talking, jittering). Take a few steps to defeat those demons beforehand - exercise rigorously the morning before your interview, this will clear your mind and stabilize your metabolism, which helps control sweating problems. Learn some deep breathing exercises if you need help calming down beforehand. Never, under any circumstances, drink a "Double Vente Latte Machiatto" or other "energy drink" less than an hour before the interview. All that caffeine will lead to a panicky interviewee that talks WAY too fast and incoherently, and that is trying to hold their bladder for an hour. Nothing good can come of that.
9. Sleep well the night before. Don't study your "interview cheat sheet" late into the night. Go to bed early, and go to bed with a clear mind. You will not sleep well if you spend the night ruminating over those questions and answers. In fact, I understand that taking an over-the-counter aid (if you are healthy enough) can help. Seasickness medications such as Bonine can clear nausea from "stomach butterflies" that might precede a stressful interview, and also have the nice side effect of being a sleeping aid (causes drowsiness). As always, check with your doctor before taking something like that.
10. Smile. The interviewer is not only looking to see if you know the technical answers to their questions, they are also evaluating whether they would want to work with you on a team or not, and if you know how to enjoy working with others. When interviewing, the measuring stick I often use is to ask myself "Would I be comfortable having a beer after work with this person?". You might be surprised how often the answer to that is "no" (especially in the ultra-bizarre circus of tech workers).

And here is a "bonus" tip submitted by David Daughtrey...

11. Dont eat at the Wing Factory on the night before an interview. Or any hot wing establishment for that matter.