Choices, choices...
Choosing a subject
Picking a subject to apply for at Oxford can seem like a tough decision. Some people have spent their entire lives obsessing over Chemistry or preparing for Medicine, but for the rest of us, several subjects can often look interesting or appealing. Every Oxford degree shares an incredibly high standard of teaching and career prospects that are among the best in the country, but here are a few things you should be mulling over while you scroll thoughtfully up and down the "subject" menu on UCAS.
Entrance requirements. It doesn't matter if you were born with a transmission electron microscope in your hand and an equation in your heart: if you don't have A-level Maths, Oxford will not consider you for Physics. You can find information about what each subject requires on this page: http://www.ox.ac.uk/admissions/undergraduate_courses/courses/index.html
Are you really interested in the subject? Studying anything at Oxford involves not just a lot of work, but a lot of thinking about and around your subject. If you choose a subject you aren't genuinely interested in, you are in for a grim few years - even if you make it past the interview, which you won't. Being interested in your subject doesn't mean knowing it all before you come - otherwise there wouldn't be any point studying it! Most courses assume no prior knowledge, but tutors look for a keen enthusiasm towards the subject.
What it's actually like at Oxford. The same degree can be very different at different universities. An Oxford French degree will involve a lot more emphasis on literature, and a bit less on language, than those at most other universities. An Oxford Computer Science degree will tackle the subject in a much more theoretical way than you might be expecting. You can look at the course structure of Oxford degrees at the link above, or see what each department has to say about its undergraduate course here: http://www.ox.ac.uk/divisions/department_az.html. Best of all, you can go to a subject open day, which should give you a really good feel for what each course is actually like.
The sheer variety of degrees on offer! As well as the obvious subjects you'll have studied at school - English, History, Biology and so on - Oxford offers many you won't have encountered before. Some of these are "joint schools", multiple-subject degrees like PPE (Philosophy, Politics and Economics). Others are just not on offer at school level. These range from the obvious, like Engineering, to the really quite unexpected, like Ancient Egyptian Studies. Make sure you've considered every option available to you, or risk spending the rest of your life feeling pangs of regret every time a new installment of The Mummy comes out.
Choosing a college
Unlike choosing a subject, the truth is that college choice actually doesn't matter all that much. Once you get to Oxford you'll start to feel proud of your college, and partake in various petty rivalries - St Anne's has a long-running if completely pointless disagreement with Wadham. But your social experience at each one will be fairly similar, and because teaching is organised at faculty level, there's really no difference as far as academic matters go. Every college provides a library, a common room, and a wide range of sports facilities. You'll never feel left out just because of the college you chose (unless you go to Wadham, because it's rubbish).
So, what should you base your choice on? It doesn't have to be anything deeper than liking the look or feel of the place if you get a chance to see it yourself. The colleges do look quite different, and some have unusual facilities. St Anne's has a student coffee shop, Magdalen has a deer park, and Wadham, whatever its faults, has a college bar which opens at 1PM. You could also have a look at their policies for accommodating students, which can vary quite a bit.
Finally, it's worth remembering that you don't have to choose a college at all! About one-fifth of all Oxford applicants make an open application, and are assigned to a college at random. Once they arrive at the college they've been allocated to they fit in just as well as anybody else. If you're really finding it hard to decide on a college, you might well prefer to send in an open application rather than waste any more time agonising over it.