I am posting this in the hopes that some of you are looking for work and will have the opportunity to attend interviews.
1. Before the interview, learn a little more about your potential employer's history and/or culture.
This will help you get a sense of how you might (or might not) fit into the company by understanding its core values, and allow you to ask intelligent questions about the job (e.g. how your role fits into the bigger picture).
2. Relax and don't be nervous.
This can be hard, especially if it is your first interview, or you are being interviewed by more than one person at once.
All you can be expected to do is your best in preparing for the interview and writing the job application. As long as you have done your personal best, you cannot improve your chances by worrying or getting nervous.
In one of the first interviews I attended the interviewer said to me "It's good to see you." I got so nervous that I thought he said "How are you?", to which I promptly replied "Good."
And then, an awkward silence followed...
3. When in the interview, concentrate on the interview (e.g. switch your mobile phone to silent).
If you do have to take a call due to an urgent reason (e.g. family emergency), explain why you have to take the call and people will usually understand.
But don't fail to pay attention during the interview when you are being asked questions, or pretend that you are still listening when you're not.
My boss conducted an interview some years ago and the guy being interviewed started replying to a text message on his mobile phone under the desk. He wasn't paying attention, pretended to be listening, and thought nobody could see him texting. Needless to say, my boss was too eager to wrap up the interview.
4. Answer the question
Yes, it sounds obvious and it should be...
But, in one of the interviews I conducted, this guy kept telling me about something totally irrelevant to the question I had asked him, and kept repeating the irrelevant statement even when I asked him other types of questions. He then proceeded to ask me if I had any other questions for him!
If you are asked a question, but do not understand it, it is okay to ask the interviewer to clarify the question before attempting to answer it.
5. Honesty is the best policy
You may really want this job ... and may be tempted to fudge the facts a little to do better in the interview. But, resist the temptation. It may get you the job, but it won't earn the respect of your co-workers.
That said, you can show your keen interest by admitting that you may not have all the required skills, but learn quickly and are prepared to work hard.
In many cases, employers not only look for someone with the required skills and knowledge, but how the potential employee is as a person, whether you are a good fit for the company, your personal values and ethics, and any other 'hidden' skills you may bring to the company (e.g. strong customer service focus, ability to multi-task, deep knowledge of some obscure tool the company has that no one seems to know how to use, etc.).
So don't rule yourself out just because you don't have 100% of all the advertised skills.
These tips are from my personal experience or having direct secondhand knowledge, so they are limited in scope, but I still hope they will be useful.