How to get into Cambridge University if you go to an American school?

Hey, I want to go to Cambridge University, I live in Engalnd, about half an hour away from Cambridge. I am attending high school at an american school on a military base (RAF alconbury). Since i don't have GCSE's or A levels at my school ehre is a plan I came up with that I think should get me into cambridge: Do sports all three seasons,and extracurricular activities, Volunteer work, Organize events, get a 4.0 average or more (All A's), By senior year take 3-4 AP classes, get a good SAT score, and join clubs. Is there anything else I should do?