A couple pieces of great advice I came across on these colleges' websites today:
When making curriculum choices, always seek out courses that will enrich and challenge you, rather than thinking about how they will look to a college application reader—every college reads applications differently, so it’s difficult to predict what will look “good” to every college.
University of Chicago
Our hope is that your curriculum will inspire you to develop your intellectual passions, not suffer from unnecessary stress. The students who thrive at Stanford are those who are genuinely excited about learning, not necessarily those who take every single AP, Honors, or Accelerated class just because it has that name.
Some applicants struggle to turn themselves into clones of the "ideal" MIT student – you know, the one who gets triple 800s on the SAT. Fortunately, cloning is still for sheep. What we really want to see on your application is you being you – pursuing the things you love, growing, changing, taking risks, learning from your mistakes, all in your own distinctive way. College is not a costume party; you're not supposed to come dressed as someone else. Instead, college is an intense, irreplaceable four-year opportunity to become more yourself than you've ever been. What you need to show us is that you're ready to try.
This process of preparing for college can be equal parts fun and frustration. Try to focus on the former.