I arrived at the porter's lodge and was instructed where to go by the porters, I then waited in a room with other interviewees until my first interview started. I had 2 interviews, each was 30 minutes. The first was with one interviewer and was about physics, the subject I had indicated I was most interested in. The second was with 2 interviewers and covered the other natural sciences subjects I had expressed interest in.

In the first interview I was asked exclusively physics questions, these were difficult but even when I was giving the wrong answers the interviewer was keen to guide me through to the correct answer (I insisted on the incorrect answer to one question multiple times before I figured out my mistake).

The second interview was a little more disparate the questions I can remember were about trigonometry and then some integration and curve sketching followed by some materials science about molecular bonding. These happened to be things that I was slightly more familiar with, especially the maths, the interviewers realised this and quickly moved into related but more complicated problems.

Reading the recommended books, especially why chemical reactions happen. I also had practice interviews from school which was helpful as were the extra classes that I had for the various Olympiads (maths, physics and chemistry) that I did, as well as STEP and the Oxford physics entrance paper (I can't remember what it is called)

Everyone finds things that they think they did wrong in the interview so don't worry about it after it is done. As I said I was very insistent on a wrong answer (and most people I have talked to have similar stories).