Have an Answer?
I think one of the best ways to be more confident is just to practice. Get a list of common interview questions and answer them out loud as many times as it takes to be natural. If you are applying for a specific job, think about what questions they might ask. Take the time to practice explaining about a student group or internship you've done. It might even help to record yourself with a camera (even a laptop webcam!). See what fillers you use and where there might be more room for improvement.
I completely understand where you're coming from. Although some of us are quick to answer and we feel like we know exactly what to say, sometimes we need to wait just another second before responding. ex: on interviews we want to sound perfect. But, once you are asked a question make sure you have all of your thoughts and words together. Take your time, don't be long winded but relax. Speak clearly and profoundly. Don't sound like you're asking a question when in fact you're stating something. Walk and talk with confidence and strength!
Getting tongue tied happens and the best way to avoid is practicing certain lines over and over again and making it yours. Its like reading a script and acting out the part. Several videos are online (youtube) for interview questions and that can prepare you for those famous interview questions.
Interviews can come in multiple forms, but usually an interviewer is trying to understand either your experience and skills, or to assess how you will behave in certain circumstances (like when you're faced with a challenge). If you're going into specialized fields like management consulting or business strategy, you may find a third type of interview where you must prepare a case study or other formal presentation. For any of these, preparation is important.
One thing you should always have prepared is a 30-second overview your background, your skills, and what kind of position you're looking for. It should be well organized and practiced so that you can confidently mention who you are and what you'd like to do.
As other people have mentioned, confidence in your interviews is often about practice, practice, practice. If you can find someone to practice playing the role of the interviewer with you (as silly as it may feel or sound) it will give you the real-world feeling of being in the situation and, with practice, you'll learn to anticipate questions and your own answers so you'll feel more comfortable.
If you're already in a job and are just uncomfortable with people in positions of authority, one thing that always works for me is to find some common ground with the person and connect with them on a personal level, when appropriate. Maybe talk about the framed photo of a dog on your boss's desk ("Oh, is that your dog? What's its name? How long have you had him/her?") - often that will ease any tension you have and help you see that a superior is just a person too.
We have also figured out that your body language and posture can change how confident we feel, and can even change your body chemistry! Here's a link to a speech about this:
The key to getting more confidant is lots and lots of practice.
Practice with your family and friends.
If you are still in school, ask around the career center or advising office to see if there are any interview workshops or mock interviews coming up.
If you find yourself nervous around people outside of the interview setting, practice talking to strangers. Go to a mall or an outdoor market and strike up conversations with people.
Even your interviews are practice. Sure you may have botched one, but was it better than the last one you went to?
Confidence builds with time, you can do this, I believe in you!
When you know you have an interview coming, it's time to practice.
Start with writing down you answers to these basic questions. Typical questions:
Tell us about your self?
Why do you want to work here?
What is your best asset?
What do you like the least about yourself?
Now sit in front of a mirror. The mirror is the interviewer. Now practice. Read your answers, then re-read them, try again and again, until you are comfortable.
By having some standard answers ready you will be more confident and more prepared.
And if you don't have answers to all questions, your interviewer will not be surprised. They have all sat in your chair and they know it can be nerve racking.
Remember to breath, breath, breath.