1. Focus on the positive.
Positive talk appeals to why you want things (‘challenges’, ‘opportunity’, ‘career development’, ‘community’, etc), what you have to offer (‘professional skills’, ‘vision’, ‘focus’, ‘innovation’). Negative talk simply tells the organization what you are likely to say about them in 6 months. You are looking for a (new) job because it will make you and the world a better place.
2. Be professional.
Dress and talk as if you know what it means to be a professional. That usually means you dress inconspicuously. You don't want the way you dressed to be what people talk about later unless you're in the fashion industry. Being professional means you know about the issues related to your field or area of expertise. Professionals don’t know it all and they aren’t trying to be your lifelong bud. Humor is good, even important, but recognize that it isn’t the main show. Your oddities should also not be the main show. Leave issues that might divide the room for later, after you get the job. Focus instead on what you know about the job.
3. Know why you want the job.
Know why in the short term, in the long term, and why it fits with your career goals. This comes up in almost every job interview, whether you recognize it or it. It is the "Why us?" question. What does this job have to offer you? If you look into this by researching the organization (see point 6 below), you won't need to lie (which you shouldn't do anyway for a variety of reasons).
4. Create alternatives.
You create alternatives by applying at multiple places. A wise woman once told me to apply to many places (as many as you can imagine that are within your career goals). You can't possibly know how much you would like working in a town you've never been in or in an environment that you've never worked in. The closest you can get to knowing is to apply. So aim high and low, and get some choices. You have very little to lose and a lot to gain. You might have to say 'no thank you', but you'll learn a tremendous amount. You will get better at interviews the more you experience them. And if you get two job offers at once, then you can choose and/or negotiate a better deal. Create choices and you create opportunities.
5. Practice, practice, practice.
Practice answering interview questions. Practice giving talks. Practice talking about your past achievements. Read books or web pages on how to give good interviews and how to answer hard questions. "Why do you want to leave your current job, isn't it great?" "Why haven't you been more productive?" "What do you hope to accomplish in the next five years?" "What's your biggest weakness?" Practice answers to interview questions and have one to three points to make for each question. This keeps you from talking forever, it will make you easy to understand, and it sends a signal that you have organized thought processes on these often complicated issues.
6. Do your research on the job and the organization.
Know the competition, the goals of the industry, how people in your job are promoted, the organization's history, who you might work with both inside and outside the area you might be hired in. These aren’t all things to say in the interview, but they help make you sound confident and serious, they help you understand the context and situation, and they help you to ask better questions. They also help you be like someone they’ve already hired, which is exactly what they're looking for.
7. Know what you have to offer.
Determine what aspects of you the organization is looking for. What is your skill set? How will you succeed in this job? What do you offer that other people don't? Almost every good interview will at some point ask the question "Why you?" If you're being interviewed, chances are that the organization already knows why. You can stand on your strengths, but you need to know what they are and be ready to repeat them.
8. Ask questions (even if you think you already know all the answers).
Be interested. Practice some questions if you're not good at it. Ask your dog if you must. Recognize that these people have chosen this as their career. They want to feel good about it and you can help them to do that by being professionally interested. Questions will allow you to have a conversation and to discover common ground. They can also help you to sound more professional. "How do you see the department growing in the future?" "What are some of the biggest challenges facing the department right now?" Asking questions enriches your interaction.
9. Take your time.
1) If you put yourself out there and you do your homework, you will eventually find something that works for you. A career is a big commitment. People who look longer and harder for things are more likely to find what they are looking for than people who don’t.
2) Take your time when answering questions. Don’t be automatic, be thoughtful.
10. Leave them wanting more.
Check your ego at the door. You’re just a person. They are just people. Overwhelming people with how awesome you are is impolite. If you're really awesome, it will be obvious. Give them enough to ascertain that you’re above threshold and have a lot more to offer. You don't need to hide things, but you can't communicate everything in an interview and if you try you may find yourself saying things you later regret.
Final note: Many job interviews are just Turing tests. They are a test of whether or not you are human enough to work there. You might be competing against someone who is a better fit for the job than you. You just as easily might be the best candidate. But chances are the difference between you and the best person for the job is not something you're going to fix at the last minute. Be your best you and prepare accordingly (see above).