It all depends on the job you're interviewing for and the person(s) who's interviewing you. Do not pretend to be someone you're not and also don't try too hard. The employer will see right through you. I know it's cliche, but you have to be yourself.
As long as you're dressed well, prepared to ask a few questions, and honest you'll be fine. Confidence is a must. If you go in there looking like a scared puppy, forget about it. You also have to smile from time to time, naturally that is...not forcefully. Also, give eye contact but don't stare into their soul. You'll have to speak clearly as well. Don't talk too fast cause that shows you're nervous.
Oh, try not to talk too much either. Remember, you're not interviewing them. Definitely do not be late for an interview. Get there at least 10-15 mins early, and make sure to bring resumes and references in case they ask you for them. Lastly, don't forget to follow up. I got my current job with following up. I had to call twice before they called me back. Don't wait to hear from them especially if there are other people interviewing for the same job. Then it will be too late.
You'll have easy interviews and somewhat difficult ones. So, good luck to you.
Try to avoid asking about wages though as that might just indicate you are only interested in the money.
This is a crucial mistake. I've made this one. The interview was going well until I asked how much the job paid. His smile went to a frown and I knew I was done.