What schools are you thinking of? There is so so much diversity among UCs and T20s, and they’ll each offer a completely different experience. Assuming you haven’t been able to visit any US colleges, have you visited any in your home country just to get a general university vibe? Your chances at any one school will increase dramatically if you can provide a strong response to the question of “why this school.” As a starting point, I’d look up professors in your area of research, and you could write about them in an essay, or connect with them to talk about their research and school.