If you have decided that you are aiming for a place at either Oxford or Cambridge (remember that you cannot apply to both) then you will need to submit your UCAS application by October 15 and you will need to promptly begin preparing for the Oxford or Cambridge entrance examinations. In fact, if you know what you are applying for at which university, then the earlier you get started the better, preferably in the Lower Sixth or 11th Grade. Dependent on the university you are applying to and the subject you wish to study, there will be different entrance examinations. For the Oxford entrance examinations please follow this link and for Cambridge this link.
At AGF Tutoring, there are tutors and consultants who have graduated from both Oxford and Cambridge, and who actually sat and successfully passed the Oxbridge examinations. Therefore, they are in a particularly good position to advise and tutor you with regard to the specific entrance examinations.