2x interviews in one morning
First interview: asked about favourite subject and what was being studied at school; Second interview: given an article and asked opinions.
Reading about the subject making sure you're familiar with those books; mock interviews if available
Take time to think
Remember this advice isn't official. There is no guarantee it will reflect your experience because university applications can change between years. Check the official Cambridge and Oxford websites for more accurate information on this year's application format and the required tests.
Also, someone else's experience may not reflect your own. Most interviews are more like conversations than tests and like, any conversation, they are quite interactive.
My interview was in January, I was in my final year of school. I arrived the day before the interview as I had travelled from Scotland, and stayed the night in college. On the day, I had breakfast in college
The first interview was with one politics professor. I was surprised that she didn't ask me about the books that I had said I'd read on my personal statement, or about the school history essay that I'd brought along as an example of my work, although she did ask me about my favourite subject at school (history), what I was studying currently in that subject, and we had a conversation about that period.
She asked very general questions about my opinions on things like power in the specific periods. She finished by asking about
The second interview felt less formal, with two professors. In the interview I was asked to read an article and discuss my opinions on it.
To be honest the most useful preparation I did was probably
Other than that, I made sure that I was as familiar as possible with the books on my personal statement (I made sure that I had read at least a few chapters of each and could say something about each). I also did
Don't be afraid to pause and think about the question that they have asked. You don't need to fire back a response straight away.