Natural Sciences Admissions Assessment (NSAA), 2x interviews
Questions about physics, maths and chemistry
Practice talking, including explaining physics concepts and questions. Being genuine in the interview.
Practice papers and other similar questions
Work hard throughout the year
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: 1 min
Length of interviews: 15 mins
Online interview: Yes
They didn't ask about my personal statement, or anything else personal about me. They only asked me questions about my subjects. Although I made it clear in my personal statement and application that I only applied for physics and maths, they asked me some chemistry questions as well, although they asked about the chemistry that most applies in physics.
I practiced talking about myself and the university. I practiced explaining physics concepts in person and solving questions.
The best thing I did was remind myself that I had to be myself and not lie or give the answers I expected them to want to hear. Most of my preparation didn't do all that much as they only asked me to solve problems, but being myself I think definitely helped.
Practice papers, practice papers from a different type of test that were still useful
Don't stop working after you get your application accepted. Work still has to be done to get into the university afterwards. Sounds obvious but I relaxed after my offer.