Natural Sciences Admissions Assessment (NSAA); 2x interviews.
Interview 1: Personal statement questions, math and mechanics problems; Interview 2: Multi-part problems in physics and chemistry.
Practice questions on isaacphysics.org.
Doing past year papers in a timed setting.
Become more confident solving difficult subject-related problems, and enjoy your interview!
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:
Number of interviews: 2
Time between interviews: About 2 hours
Length of interviews: 30 minutes
Online interview: No
In both interviews, there were two interviewers and myself in a small classroom.
In the first interview, I was first asked to talk shortly about my interest for the subject and what I see myself doing in the future. The interviewers had picked up on a part of my personal statement that they were interested in, and I was happy to talk about my involvement in that science project. After that, they asked me to solve a few short problems in math and mechanics - these were quite simple.
In the second interview, I spent half of the time discussing a problem in physics and the other half on a problem in chemistry. The problems were longer and one part lead to another. If I was unsure, the interviewers would provide hints to keep my thinking going.
Both interviews were, in the end, quite enjoyable and felt shorter thsn they were.
I did online practice questions on Isaac Physics (isaacphysics.org), and other challenging problems that developed my skills to think outside the box.
I didn't know of anyone who had ever had a Cambridge interview (or anyone going to university abroad in the first place!) so my focus was mostly on the substance and not on how to 'perform'. Fortunately, the science intetviews were indeed substance-based, and the interviewers were really sympathetic if I was not super fluent in my presentation.
I wasn't really sure how best to prepare and information about the exam was hard to come by.
Looking back, doing old exams in a timed situation was definitely the best way I prepared - I believe the old exams were available online for free.
In the sciences: focus on problem-solving and becoming confident in solving very hard problems. This way you will perform better in the stressful interview, even if the questions there aren't as difficult as the hardest problems you have solved.
Also, enjoy the experience - it really is a privilege just to experience Cambridge for a day!