Common App mistakes to avoid are honestly way less dramatic than people make them sound, but a few of them almost got me. The biggest one for me was waiting too long to look at the full application as a whole instead of school by school.
I had decent essays, but my activities list was repetitive, my honors section was weaker than I realized, and one short answer basically repeated my personal statement. Another mistake: I kept editing in different docs and almost pasted an older version into the portal.
What helped was doing one full read like an admissions officer: profile, activities, honors, essay, supplements, everything in order. That made it way easier to catch overlap, awkward wording, and places where my application did not feel consistent.
If I could redo one thing, I would have started final review a week earlier.