I kind of wish I could put down all the stuff I do, because I'm (evidently) a really good interviewer. Here's some of the stuff I know of, though:
Practice body language. It might not make much sense to some of us, but body language is a huge thing. Convey that you're relaxed and confident, instead of nervous or fearful, and you'll be more likely to get the job. It doesn't have to be complex stuff -- just the basics, like trying to not cross your arms over your chest, keeping your shoulders back and your back straight, and other "open" postures, are usually enough.
Dress nicely. If you don't know what's "nice enough," don't be afraid to ask. Try to dress a little more nicely than the workplace expects employees. Ie - if the workplace is casual, try to dress in a nice polo/blouse and slacks/skirt; if they're business casual, go for a relaxed suit, etc. Going overly dressed, if you know the employee dress code ahead of time, can also be a downfall, though. If the employees are wearing shorts and flip flops, then you're likely to be out of place in a suit and tie (it may not cost you the job, but it can stand out as not being a fit culturally).
Practice interviewing. This one can be hard, but try to find a job coach that can practice interviewing with you. You can also "practice" with jobs that you might not particularly want. Still do it as though you'll want it (worst case scenario, you get a job offer and face the choice of turning it down). The more you do, the more comfortable you'll be in them.
Prepare short narratives and answers for the typical questions. Most places will ask some pretty cookie-cutter questions - Why'd you leave your last job? Why do you want to work at the new place? What's a moment on the job that you were particularly proud of? How did you handle a hostile coworker? Things of that nature. Most interviewers love stories, but make sure you practice them ahead of time, so that you don't end up rambling for extended periods of time. Aim for 2-3 minute mini-stories for most answers that require narratives. Also, come up with politically-correct answers to the questions like "why'd you leave your last job?" They don't want to hear that you got in a fight with your boss over the color of the text used on the banner. Instead, just say something like "the company was going in a direction that no longer aligned with my ideals," or something similar.
If you have a large employment gap, mention what you've done during that time. You shouldn't be sitting at home, moping. If you have a large gap in employment, make note of the things you've done to better yourself, such as continuing education, volunteering, freelancing, etc. Those things show initiative, teamwork, etc. If you're still currently looking for work, make sure to get involved in things that align with your job goals -- go to local interest meetups, for example.
Take a folder. Most recommendations are to take a folder for extra copies of your resume, but I've found that to be largely unnecessary. Perhaps bring one or two copies, but they usually have copies for everyone else there. Instead, take paper that you can take notes on, that have the questions you've compiled, or a checklist of things to remember. Keep them in your folder. The other people don't have to see what's in it, and you look more professional that way.
Compensation. I generally wait until the company asks me about compensation to bring it up. From there, instead of giving them what I currently make (or made in a past job), I give them the number that I'd like to make in the new position. Always go higher than what the minimum you're willing to take. Part of the negotiation of salary is meeting in the middle -- the company is going to open with an offer lower than what they're really willing to pay -- from there, you both "settle" for the final pay, which should be the pay you're looking for. Also, remember to factor in other benefits, such as the ability to work from home, unlimited paid time off, onsite medical or fitness facilities, etc. when considering a job. You might be willing to take a slightly lower pay if it means free access to a pool, for example.
Culture/environment. Keep an eye on how the interviewers respond (admittedly, some are harder to gauge than others), and how they handle themselves. Is there a lot of banter? Are they super-serious? Are they more Type-B personalities, or Type-A? Do you feel rushed through the interview? Do you feel comfortable and welcome being there? If/when you do an in-person interview, ask for a tour of the office, and see what the environment is like. Is it quiet? Are the cubicles/offices decorated with employees' personal items? Do the employees look relaxed (sitting back in their chairs, smiling, maybe chatting with their coworkers), or stressed (scrunched up, not really acknowledging the presence of others, working really fast)? Is the lighting adequate and is there a lot of natural light? Is there evidence of physical accommodations for people who need it?
Asking questions. I'm terrible about this one and don't generally have many questions, and the ones I can come up with are often answered through the course of the interview. Keep in mind, though, that the interview is not one-sided -- the company has to convince you to work for them just as much as you have to convince them to hire you. Once that really sunk in, some questions came more easily, because I realized that I was "allowed" to ask them. Some basic questions, though, can include things like "what's your typical day like?", "how much overtime generally occurs?", "what's travel like?" (if travel is part of the position), "what's included in the relocation package" (if relocating is a requirement), "can you give some more details about what I'll be working on?", "what is the policy on working remotely?" (though I've found that if I have to ask this question, the company's probably not all that open to it), or "how flexible are the hours?". If you don't have any questions, you can say something like "no, the ones I did have were answered through the course of the interview" or "not at the moment, you've provided a lot of information already, and I could use some time to process it all." Often, they'll offer to let you email or call them if you do come up with any, and by all means, if you do come up with a question, feel free to use that contact point.
Things you should know going in. They generally expect you to know a little bit about the company going into a face-to-face interview, but they're more lenient in phone interviews, especially ones set up by third party recruiters. If you know ahead of time the company you're meeting with, then at least peruse their website and get an understanding about what they do. Take note of any big things that happened recently, such as awards or acquisitions. If you notice something that stands out to you, such as something in their corporate philosophy, make sure to note that, too, and mention it during the interview. These things show you're paying attention, and show that you found something that was meaningful to you (which suggests that you might be a good culture fit).
If they give you a test, don't fret too much over it. This could be anything from the logic games, to a written test of some sort, to a "code day" or similar thing. Usually, they're not looking for perfection, but rather to see if how you think is in line with what they're looking for, to see how you solve problems, and how you work under pressure. Try to stay relaxed, and use the tools they give you. I know the logic games I've had to do, they allowed me to talk it out or write it out on a whiteboard.
Don't put too much stock in landing a particular job. This is probably actually the hardest thing I've had to deal with. I've gotten bites from some pretty big players in my industry, including a couple of Silicon Valley companies. Those big ones were some of the ones I failed most miserably at, because I put a lot of stock in getting those jobs. You know what, though? They're a company just like any other. Yeah, it'd be cool to work there, but some of the coolest places I've found to work are the ones that you've probably never heard of (hell, are ones I had never heard of, until I interviewed with them). I've also had to deal with this when I wasn't working and needed to get a job to help keep the roof over my head. The stakes are high, certainly, but you have to convince yourself that there will be other opportunities. If nothing else, bluff to yourself so that you stay relaxed. It's the jobs in which I was relaxed in the interviews that I got offers for. This one only really gets easier when you start getting a bunch of leads and you're not scraping for something, I'll be honest, because it's easier to know from the stack of emails and voicemails for various positions that you're a good potential fit, than it is when your inboxes have nothing but cobwebs.
That's about all I have that I can really convey. I've found that I can instinctively gauge how an interview went, and can usually pinpoint what probably went wrong, in some cases as soon as it happens (it's the one place that I can actually do that, I think because it's pretty scripted), but I know some people can't do that. All I can say is to practice and find someone that can coach you and point out some of the bigger blunders so you can work on them. They can also help you after a "real" interview to find out where things may have gone wrong.
If anyone has questions, though, I can try to answer them. I've done a lot of interviews, so I may be able to help.
