My most important interview tip: stop talking.
When you've answered the question, stop talking. There'll be a slightly ackward silent pause, but you don't need to fill it.
I'm not saying be curt, but when you've adequately answered a question, stop. Your answer to a question should rarely exceed one minute.
Be prepared for open-ended and vague questions such as, "Tell me something about yourself?" Your answer is to be one minute long. "I was born in U, grew up in V, and graduated from W High School. Since then, I've been doing X. I really want to go to college because Y and I want to do so on a military scholarship because of Z." One minute.
One of my favorite interview questions to ask is, "What is your favorite pizza topping?" I don't really care. It doesn't matter what the answer is. Everyone has a favorite. Just say what it is. What I don't want is, "Oh... I don't know. Sometimes I like sausage. Sometime I like peppers. Mushrooms can be nice... I'm sure I like whatever you like." Don't be wishy-washy and don't try to please me. That's not the question. Just say, "I really love X on my pizza."
And, as Mr. SpookyPistolero wisely advised, dress and act well and watch your language.