Unfortunately, job interviews can be far too varied to give good universal advice for. Check out Wikipedia's entry to see just how varied they can be. So instead, here's some generic advice:

• Come dressed just a little bit nicer than you would expect to come to work
• Show up early
• Do the things your parents always nagged you about: sit up straight, make eye contact, and speak up
• Don't take any part of the interview personally; it's going to be a fairly standardized process from the interviewer's point of view
  
• Research the company/organization in advance, and come to the interview with questions about both the company and your desired position
• Practice answering common interview questions, but only to the point where you feel confident in your general ability to answer them. Don't practice so much that you sound rehearsed.
• In particular, make sure you have an answer for anything that may seem negative on your resume, such as an employment gap or a period when you switched jobs frequently. Don't be defensive; just be aware that your potential employers will want some kind of explanation.
• After an interview (particularly one that felt positive), send a short personal note to each person involved in the interview, thanking them for their time.

Telephone Interviews

Telephone interviews can feel less serious, but they can actually be even more important for the time involved. Some organizations will use telephone interviews as a winnowing tool to get a pool of candidates down to a more manageable size. If pre-scheduled, prepare for a phone interview in the same way that you would prepare for an in-person interview: dress up, be ready to start a few minutes early, and do your research on the potential employer. Make sure to answer the call while in a quiet area with a good phone connection. If the call comes while you are in a noisy place or an area where your cell phone signal is poor, explain the situation and (if it cannot be fixed in less than two minutes) ask to reschedule the call.