How can I do well in interview?

Oxbridge interviews are not meant to catch you out or test your knowledge, but simulate a tutorial/supervision environment to see how you react to it and to see how you think about tricky questions. It is important to 'think out loud' - don't be afraid to make a point you think is weak, and then refute it later. It is important important to stay calm and have confidence in yourself, since if you appear nervous in a tutorial situation the admissions tutors might think that the tutorial system does not suit you.