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Well, here's a tip for you. Almost every laptop computer made in the past few years has a web cam and you can buy cheap web cams that will suit your purpose for desktop computers - so use it!
Just turn it on, minimize it, and then answer a question!
Why minimize it? Because you don't want to be looking at yourself as you answer the question. Look over your computer or past your monitor as you answer and pretend you're in an interview. Try to be in depth but don't babble.
Practice answering questions and you'll see what the interviewer sees. Are you gazing nervously about the room? Are you twiddling with your hair? Are you repeatedly clicking your pen? These are all things that the interviewer will notice and that may negatively impact the interviewer's impression of you.
Also, listen to yourself. Can you clearly understand what you are saying are do you have ups and downs in your speech that make it difficult. Do you have lots of ums and ahs that distract from what you are saying?
If you do, keep practicing until you have it right!