Colleges look for three things in your admission essay: a unique perspective, strong writing, and an authentic voice. People in admissions often say that a great essay is one where it feels like the student is right there in the room, talking authentically to the admissions committee!
Admission essays are very different from the 5-paragraph essays you write in English or history class! Great essays are built around stories, not arguments. They reveal your character, not rehash your achievements. The best essays focus on moments when you changed, learned, or grew as a person.