Natural Sciences Admissions Assessment (NSAA); 2x interviews.
Interview 1: discussion of a topic taught by the interviewer. Interview 2: discussion of a topic related to the course.
Mock interviews, revising A level content, reading articles beyond the syllabus and preparing to talk about topics of interest.
Practice papers.
Do readings, research and projects on topics in an area of interest related to the course.
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: Natural Sciences Admissions Assessment (NSAA)
Number of interviews: 2
Time between interviews: 10-15 minutes
Length of interviews: 30 minutes or less
Online interview: Yes
In the first interview the interviewer asked me about my interests and discussed with me a certain topic that they taught. They asked me some questions that they didnt expect me to know but I might have come across in my background reading. The interviewer asked me to think about those topics and discussed with me my thoughts. I was a bit nervous and missed a question or two that I wouldve gotten if I was more relaxed.
For the second interview, they asked me briefly why I wanted to study my course then asked me about an extension topic, but luckily I already knew a lot about this as it was in my area of interest, so we were able to have a very good discussion about this. Very importantly, when I had a point of view, and they challenged it, I was able to respond to that and see how their opposing point of view was valid and change my mind.
I went to the Oxbridge
I also had to revise a lot of my A level content because I realized that I had forgotten a lot of it around the time of the interviews. I also made sure that I had done plenty of reading, like a year in advance, to find topics that interest me and be prepared to talk about them in depth, but specifically 1 main topic.
Tons of practice papers
Read a lot. Find an area of interest and read about it a lot. Do research, do projects on it, then read a lot of extension articles and do mock interviews, extend your thinking beyond facts that you already know.