TSA; 3x interviews.
Interview 1: felt challenged but guided towards a correct answer; Interview 2: not very maths-y, more practical.
Re-reading/wider reading; practice interviews; develop critical thinking.
Be confident; don't worry too much about how the interview appears to go; show them how you 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.
Test taken: Thinking Skills Assessment (TSA)
Number of interviews: 2
Time between interviews: most of the day
Length of interviews: 25 minutes
Online interview: No
Each interview had three tutors in the room (each of PP and E), and we spent about 8 minutes on each subject before moving onto the next one. I had two interviews, and both economics sections were fairly practical, not particularly maths-y. Both times the chair I had to sit in was much lower than I was expecting - it was an armchair, not a desk chair as i was expecting! The tutors, while obviously pushing me on the answers I gave, were clearly trying to guide me to a good answer and trying to make me show my best side. In both PPs, I was asked a question and then each further question went into more depth on the same topic and explored different areas of the topic, and they often tried to get me to give more information on the answer I gave/ defend it against a criticism they offered.
Re-read (or in a lot of cases read for the first time) the books I mentioned on my personal statement
just banged out most of the past papers on the testing website - YOU DO NOT NEED TO PAY FOR A TUTOR!! the test is looking for quick thinking, problem solving, and basic maths, and the essay for an argument to be made and defended quickly. practice doing the test and the essay in the time, and just get used to the type of questions it asks you. for the essay, ask one of your teachers (nicely) to give it a look over and feedback.
It felt like my first interview went completely terribly, and I went back to my room and cried, but that meant I was pretty relaxed going into my second because I didnt think I was getting in anyway so I just enjoyed it. Remember that they've chosen you to interview because they can see you have potential and they want to talk to you to get to know you personally and see how you think - so show them!