American applying to Oxford/Cambridge?

As an American sophomore in high school, I was wondering what the main differences between applying to schools in the UK and applying to schools in the US are. Of course, getting into Oxford and Cambridge is no easy task, and I may just be your classic overly-ambitious teenager. So, really, while Oxford/Cambridge would be great, they’re my reach schools.

I am just curious as to what I will need to do over these next two years. What standardized tests will I have to take? Will there be less of an emphasis on extra-curricular activities? Should I be taking as many AP’s as possible? Will it be harder for me because I am not from the UK?

If this is relevant at all, I plan to study economics and French.

(being answered on your other thread)