What do i have to do to get into Princeton, Yale, or Harvard.?

I am currently an 8th grader, and while i know its a long way away, my sister (who goes to Yale currently) started working towards it around this time too. She's told me some stuff, but i would like to know more. I am currently attending Sidwell, a very highly ranked school in DC, and I get straight A's. I am in the AP Math course next year, i take squash and guitar and i am planning on joining Model UN, debate club, JCC, and outing club next year. I am on the advanced Science Track. I do not pride myself in athletics, unfortunately. I have an uncle, sister, and aunt who went to Yale, a father who went to Harvard, and a cousin who went to Princeton, so a few legacies. What do i have to do?