Just so you are aware, there is a code of conduct applicants to Oxford are required to follow and so we can’t give exact details of our interviews (i.e what we were asked etc).
I have just finished my first year of MChem chemistry at Oxford. I got in on my second attempt having been previously rejected after making an open application (I was assigned St Hugh’s as a first college and St Hilda’s as a second). I applied to Magdalen, was interviewed by Magdalen and Somerville, got an open offer from Queens and yet somehow I ended up at St John’s lol. Any advice given is based on what I did right the second time and in hindsight having messed up the first.
I personally used Olympiad round 1 past papers (and some round 2 past papers I had access to from when I got in to round 2 in 2022, but I believe these are resources that unless you are a round 2 participant yourself, you unfortunately won’t be able to access) to get practice applying what I had learnt at A level to unfamiliar situations and taught other students material from the A level course to get practice with improving my communication and articulation skills. As your interviews are only about half an hour long, you need to know how to boil down your explanations to make them as relevant and concise as possible.
I’m sure you’ve heard thousands of times that the interviewers need you to think out loud - and this advice is really important. Make sure you explain assumptions you make in calculations, why you have reached x conclusion etc etc - even if you use erroneous reasoning, you will still at least make it clear that you can at least independently think about a problem and it makes it quicker and easier for your interviewers to give you more specific and helpful prompts where necessary.
If you have any questions about my experience of the first year of the course, feel free to ask away. Just note that I’m not very active on TSR any more and so expect slow responses from me.