As someone who went to Harvard, I have no clue how I got in; my test scores and grades were at the Harvard median, but I was much less impressive than most of my classmates.
I would approach the admissions process as I did: just do your very best in high school (or college, for grad school admissions) and apply to schools that you have a shot at getting into, but don’t pin your hopes on a specific school.
I NEVER expected that I’d end up at Harvard and was shocked and thrilled when I got in.