Take tough classes. Interrogate your beliefs and presumptions. Pursue knowledge with dogged precision. Because it is better to be educated and intelligent than not.

This cannot be understated. Don be wanton or careless or cruel. Treat those around you with kindness. Help people. Contribute to your community.

Find what you love, and do it. Maybe its a sport. Maybe its an instrument. Maybe its research. Maybe its being a leader in your community. Math. Baking. Napping. Hopscotch. Whatever it is, spend time on it. Immerse yourself in it. Enjoy it.

Your application is read by a senior staff member who will look for deal-breakers (like a bunch of D's, for example).

Assuming you're competitive, your application is then read by a primary reader who will summarize it at length for the committee.

Then a second reader (and sometimes a third) will read and write their own summaries.

Then it will go to selection committee, where multiple groups of different admissions staff and faculty members will weigh in on it.

Assuming you've made it that far, the senior staff will then review it again.