Pause before you start talking. You'll need no more than 8 seconds to see if you at least partially answer or is it better to change the subject. Take a breath and smile at him.
Ask them to repeat the question. You may find that it contains a subtext, a hidden meaning. Or question will be complex, consisting of several parts. Specify whether you understood the essence. This will help you to win some time to think.
Talk aloud. Remember all information known to you on this matter. Comparing them, try to find the answer in a logical way. For example, the other person asked, is there life on Mars? You do not know, but begin to think of the lack of atmosphere, I remember recently read an article about extraterrestrial civilizations, etc. And you are can confidently answer: "No, it's fantastic."
Ask for some time to think, if you want to let the interlocutor in the course of his thoughts. Tell me that you understand the importance of a given issue, so you need a few minutes to articulate a response.
Admit that do not have at the moment, but you know where I can find the answer. This method will help you in difficult situations during the interview. You show yourself a man of honest and capable of self-improvement.
Redirect the question to others, ask their opinion. Perhaps those of you who are well versed in this subject and will gladly show their erudition. Or start up a discussion. In both cases you will avoid the need to answer the awkward question. If the joint efforts of the answer will not be found, try to defuse the situation with a joke about the impotence of the "collective intelligence".
Return the question to someone who asked it. It is believed that to answer a question with a question is bad form. But it's the best way to deal with incorrect questions involving your personal qualities, privacy or commercial secrets. Use simple wording: "And how you yourself would answer this question?" or "would You have told this about myself?"
Admit you have no answer, because this topic is not interesting. You may not know the name of the captain of the Brazilian national team on football, if you don't like the game and have not seen any of the match. But answering thus, try to be as polite and not to hurt the feelings of the interlocutor.