1. Where did you gain most of the information you needed to make your application?
Prospectuses, websites, Oxford and Cambridge open days - went to colleges and the medical faculties (and maths and biology!). Chatting to a few people on TSR who were already here.
My school had 'Oxbridge sessions' for those students they thought should apply, and though they meant well not sure they added a lot to my application, apart from a small amount of reverse snobbery and a large amount of anxiety.
2. What were the most important questions you had when you made your application?
Which college?
What do I wear for interview? (whatever you feel is 'professional' and are comfortable enough in to be yourself - smart trousers and a blouse seemed to work fine for me, some girls wore suits as did all the boys I met. None of my interviewers seemed fussed).
Will they try to trick me? (no, they won't!)
Are the students here going to be like the ones I met at interview? (to be fair, a stressful situation where people are preparing to 'sell' themselves but did encounter a lot of one-upmanship and 'which school do you go to? Oh, I haven't heard of THAT' which rather put the shy 17 year old me off Oxford. My fears were unfounded though; have yet to meet anyone from any background who got in who behaves like that!)
3. What do you know now or understand now that you didn't when you made your application, that would have helped you a lot. ie. what have you realised in retrospect about the process?
Pick whichever college you fancy, for whatever reason (mine=good self-catering facilities and pretty gardens). DON'T play the percentages game. If you're good enough, you'll get in to Oxford somewhere, but if you pick a 'popular' college (varies to some extent year on year), you may not end up at the one you pick.
Interviews are quite relaxed! Just a chat about quite interesting biology and medicine-based problems (and a bit about you as a person). Important to show what you're thinking and why and be prepared to (politely) defend your viewpoint, which can be intimidating when you're talking to someone a LOT more knowlegeable than you.