You must submit your UCAS application by 15th October using the UCAS Apply web link. The process from a Cambridge perspective can be found here. Note that you cannot apply for both Cambridge and Oxford.
Personal statements
As part of your application you will submit a personal statement. Follow this link for UCAS advice on writing a personal statement. This is about you and will be the same for all your applications. It is impossible to generalise on how different universities, colleges or even individual Admissions personnel view personal statements but guidelines from Cambridge are clear to the extent that the emphasis must be very much on your interest in your subject. Wider interests and achievements will only be seen as relevant insomuch as they might relate to your chosen subject.
The University offers a guide on How to write a great personal statement.
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