5 x 20 min interviews and MAT
Problems and personal statement
Practice interviews and resources from the Student Room
Practice papers
Don't be surprised if you can't answer some of the questions, as they are designed to push you as far as possible.
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: Mathematics Admissions Test (MAT)
Number of interviews: 5
Time between interviews: Variable - from 2 to 8 hrs
Length of interviews: Around 20 mins
Online interview: No
The majority of them were working through a few problems on pen and paper, with the interviewers providing tips if needed to continue the problem. Also a few interviewers asked questions on the personal statement
I did practice interviews at a local school and used resources from the Student Room website on maths interviews
Practice papers for the MAT
Mainly to do practice interviews as this will give the best replica of what it will be like. Also, during the interviews, voice your thoughts because even if you don't know the answer, the interviewer wants to see your thought process. Finally, don't be surprised if you can't answer some of the questions, as they are designed to push you as far as possible.