I applied and was accepted to read Social and Political Sciences at Selwyn College, Cmbridge. This was 15 years ago now, but I am guessing things haven't changed that much! Firstly it is important to understand that the difference between Oxbridge and other universities is that you apply to the college. Getting the right college is important as each one is very different, especially in terms of how traditional they are and how many places they have for any given subject. I chose a college which accepted a high proportion of state school students, as I was one, and had more spaces in the humanities.
The inteview is scary, but again, because I had chosed the most relax college, for me it was a laid back professor in a small room, not a bank of old men in a library!
I got offered a place but didn't meet the AAA offer. I got put in the pool. This is a bit like clearing, when the college can't offer you a place but liked you enough to think you would be a good Oxbridge student. The other colleges with spaces for the subject you have applied for then look at your application and select students to fill their spaces.
I didn't get a place from the pool and ended up going to Goldsmith's. My two best friends did go to Selwyn and in hindsight I felt not going was a blessing in disguise. The teaching process at Oxbridge consists of lectures and tutorials. You have a tutor who sets you an essay on a Thursday to be submitted on Monday. You then sit with them on the following Thursday to critique your essay. You then get set a new essay title and so forth. My learning style requires more support and encouragement and I could not have coped with being criticised as much as my friends were. I much preferred being top of the class in a good university than struggling for approval at Cambridge. My friends also struggled to get work when they left as many employers are weary of Oxbridge graduates.
My advice would be to research the colleges, and go for it if you want to, but to think about why you want to go to Oxbridge. I am proud to say I was offered a place but I applied because it was seen as the academic pinnacle, and not because it was the right environment for me.