Register for and take the BioMedical Admissions Test (BMAT) after you send in your application. Applicants are required to sit for the test after they apply to Oxford; if you don't take the BMAT, you will be denied entry.
Study hard for the BMAT. Interviews are given to candidates based on A-level and BMAT scores. The average BMAT score for applicants was 51.09. Candidates interviewed averaged 61.41. For international applicants who did not take A-levels, more weight is given to the BMAT scores.
Take A-level biology. Although the university states that biology isn't required, 93.5% of applicants had an A-level in biology, and the university states that a lack of knowledge in this area can make for a difficult first year of study.
Don't overstretch yourself on A-level exams. The typical applicant for Oxford medical school took three A-levels in one sitting and passed all three with A grades. The university's FAQ states that there is no need to take more than three A-levels: "Quality rather than quantity of study is what really counts." The university goes on to state that a candidate who is struggling to achieve A grades is not likely to succeed in their program--so take 3 A-levels and ace them.