Interviewing effectively is an acquired skill. Very few people are so talented that they can do it well the first time without much preparation. If you really want to be successful in interviewing, I recommend that you start by understanding that there are things you must do before you interview, there are things to expect during an interview, as well as things you must do to follow up after an interview.
Employers are interested in some very specific things. They want to know that you fit their needs on a variety of things. They want to know that you have the right stuff. The things that will either make or break your interview include:
Bottom line, can you do the job?
10.0 Interviews - The Essentials of Your Presentation - Part 2