ALWAYS BE PREPARED - Do your research, do your due diligence, look up all people you're interviewing with on LinkedIN, Google, Facebook and everywhere else you can find useful information. If you come in not knowing anything about the person, you're half out the door already. You've already shown laziness and lack of basic initiative, not to mention lack of interest. REMEMBER - PEOPLE LOVE TO TALK ABOUT THEMSELVES. If you get your interviewer to talk a lot about their experience in the company and life experience, in general, you will have predisposed them toward you. Use this to your advantage.
Gauge the interviewer (your future boss or colleague). What is his or her body language? Is he or she a mindful, conscientious person by appearance and speech? Does he or she pay attention? Look you in the eye when speaking? If he or she's a slob, expect the same in your interactions. Looking you up and down? Expect the ogling all the time, then. Flirtatious? Distracted? Checking the BB or iPhone every free second? You can tell a GREAT deal about a person from the first impression, which is often right on or otherwise largely so. Notice as much as you can. You've been forewarned!
Ask smart, pointed questions about the interviewer's experience in the company and before, showing you've done your research and are truly interested. The more specific, the better.
***Ask about leadership style, expectations in the first year, problems that need to be solved, skills that are necessary in the job, specific opportunities for professional development (classes/seminars/workshops/subsidies for outside learning, etc), how you can get that person promoted when you're in the job, what tools you have at your disposal to do the job, what interaction you would have with other departments and with executives, what is the person's favorite thing about the company and other people on the team, etc. The more pointed the question, the better. Get a solid sense of behavioral profile of the person, just as much as how the environment will be and how easily (or not) you'll fit.
Notice the manner - super uptight or annoyed or easy-going or anxious. This will give you a sense of context.
**WHAT DOES THE INTERVIEWER CARE ABOUT? Not so many things, it turns out. First is, do you have the up-to-date skills and attitude to do this job. Second, have you solved similar problems before. Third, are you gonna be easy to work with or not (the beer test) and can you play nice with the others. Go in ready to show all three are yes.
Don't be skewed by perks. Every half-decent company has something to offer - free coffee, massages, cafeteria, whatever. Your main concern is whether you can do the best work of your life (so far) in this context, with these people, plus whether you will add a lot of value and can make a name for yourself there (and quickly). Not all of this will be clear from the interviews, but still a lot.
Presuming you ace the interviews, ask to come and work for a day in the group. Perception and reality must meet in practice. You won't know unless you try.
Ask people you know in the company, if any, about culture and the team/department, in as much detail as possible. It should help temper your expectations. Again, DO YOUR RESEARCH. Read reviews on Glassdoor.com, take current or past employees out for coffee. Ask around. DON'T BE PASSIVE ("I just need a job, ANY job.")
Think like your future boss. What problems are there to solve right now? How do I position my team for success and growth? How do I deliver value to the company before year's end (and reviews)? Will this candidate deliver greater value than what we're paying him or her? Have they dealt with these scenarios before and successfully delivered? Can I deal with them daily? Are they trainable quickly and can they pivot quickly, as needed? Can this person communicate effectively with me and others on the team?
Answer these questions ahead of time and be ready to prove with examples from your past.
Make eye contact throughout the interview. Worst thing is to show yourself as shifty or unreliable or easily distracted.
Smile! Never hurts, always helps (if sincerely felt).
Careful with humor! Not everyone gets it or should be made to try.
Bring up anything you have in common with the interviewer (find out ahead of time). Humanize yourself! Make yourself seem more familiar! Same school or town is big, same sport or activity, same background (in some cases, but be careful) are all helpful.
Calm your nerves. Be prepared and be confident.
Open your posture. Sit up, arms and hands apart on the table (not in a threatening manner, obviously), shoulders out. Project confidence and competence. Practice the open posture beforehand (at worst, fake it 'til you make it). This also helps a lot in negotiating. You'll feel the difference psychologically and in the result.
Always be unfailingly polite - day hi to the receptionist and every person you meet. You could do a lot worse than this. Every impression is important, most of all sincerity.
Ask for a cup of water before starting the interview and see what happens. If possible, walk around to the pantry and observe how people interact in the place (at all? A lot? Are they friendly or stone-faced? Zombies?) Is there light? are there windows to look out from? What's the view like? Are office doors open or closed? What is the floor structure? Where does the boss and boss's sit? Among the workers or apart? See as much as you can of the place in the short time you have there. This will tell you how open or closed or hierarchical the place is, how much interaction there is among people, how open people are to new ideas and interactions, etc. Very valuable info.
Be concise and to the point. Have a story to tell and be able to tell it well when asked, "Tell me about yourself." This will show your personality and how put together you are (or not).
Know your strengths and weaknesses. Manage to make a strength sound like a weakness and then show how you've worked on it before.
Be ready to discuss how you've overcome adversity. Surely, there's something you can discuss without spilling out your soul completely.
Don't let awkward silences happen. Ask a good question. Turn the phrase.
Use active verbs as much as possible in discussing achievements and past experiences. This shows what you've actually done and that you're pro-active, not passive. Practice this with friends.
Not a word about politics or religion or background, unless asked (not likely unless you share one of these by background). If asked, defer. Not a word about politics or religion.
Interviewing is just as much (if not more) about finding out what YOU need, not just if the interviewers like you and whether you'll fit there. Use the opportunity well! Even if you don't get it, you learned something.