BMAT; 3x interviews.
Personal statement: books included; subject related questions; graph and data analysis. Felt guided if got stuck.
Personal statement re-read; re-read notes; mock interview; further reading and about current affairs.
Know your personal statement; take your time.
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: Biomedical Admissions Test (BMAT)
Number of interviews: 3
Time between interviews: 2/3 hours between each
Length of interviews: Two were 20 minutes and one was 40 minutes
Online interview: No
All my interviews started very casually and with a question about something from my personal statement. Both the books I had mentioned were brought up in conversation and I was asked to discuss either my favourite part or a specific part that I had highlighted in my personal statement. The majority of the interviews were taken up with subject related questions. I was often shown a graph or diagram and asked to say what I saw and why. Some interviews were harder than others and therefore harder to relax into.
I mainly focused on my personal statement, making sure that I could expand on any sentence I had written. I went over some notes of the books/article I had mentioned to refresh my memory. I did a practise interview with my friends, which wasn't too serious, but was a good way to start talking about my ideas out loud.
I did nearly all the past papers I could find on the BMAT website. I revised some GCSE content that would be needed for the science section of the paper and asked my teachers questions if I was unsure on the practice questions.
My advice would be to not over prepare as you want it to be as natural as possible, just like a conversation of discussion. I had notes of things I could say but definitely don't memorise things. Make sure you know your personal statement very well because then you can be more relaxed knowing you can talk about any part of your statement at length. If I did it again I would definitely not rush to answer questions. It's ok to ask for a minute to think about an answer.