What are the key tips you would give me before my science based Oxbridge interview?

Always make sure you have read around your subject and are up to date with any recent media reports of scientific research linking to your area of study. However, the most important thing is to have practised mock interviews and mock questions so you are familiar with the process and will be confident when attending the interview. The questions you will be asked will be difficult and you will no doubt get some wrong but make sure you are always communicating with your interviewers so they can see the thought process you are going through. After all they are testing whether you are teachable or not, being exceptionally bright but not non-communicative is not what they are looking for. Finally, make the most out of your interview and try to enjoy it, it is a once in a life time opportunity and you should see it as good practice for job interviews later in life.