I thought I might repost this post from a small thread over here:
I do think though that the importance of help fom schools might be exaggerated here - of course it's really useful and teachers who offer to help are amazing, but please don't worry if your school doesn't support you! I applied fo natural sciences at Cambridge from the Netherlands - this is particularly tricky as unis in my country don't select at all. This means most people hardly care about school and will only want to barely pass - doing better than that is seen as a waste of your time because you could be going out and hanging out with friends. Reading around your subject is even more rare - in fact, I only discovered people wrote books about science a year ago!
I often didn't feel too supported by my school, I had to sort out UCAS on my own, instruct my teachers on how to write a reference, find out how to write a PS, find books and articles to read and arrange lab shadowing at a uni (it was my countries biggest uni and not a single high school student had ever shadowed in the department before, if that illustrates my point), self-study one of my subjects because of timetabling issues (I would often find out about tests on the day because the department forgot to tell me), and self-study the biology and chemistry A levels (since I have to do many more irrelevant subjects so not all the A level material is covered for individual subjects), and practise for the admissions assessment. It was a lot of work, but the internet contains a wealth of knowledge. Applying to Cambridge is a lot of work for everyone, regardless of background.
I was in other ways hugely privileged: my parents have been to uni, they were able to support me financially without me having to pick up a part-time job or care for siblings, I never had to worry about paying UK tuition fees (which are 5x as high as fees here), and my teachers always believed in my ability to succeed.
Of course, if your school can help massively: that's amazing, it will make your life easier, and you should be very grateful. But don't fret if your school isn't too helpful and doesn't have much experience with oxbridge. You can still get in, many students will, and it will teach you determination, independence and will make you feel great if all works out. I am really grateful for my experience, it taught me so much coming from high school where you are largely spoon fed. Applying to Cambridge is less complicated than you think! Don't feel demotivated if your school won't help you.