How Do You Tame a Messy Excel Spreadsheet?

Yesterday I opened a huge Excel file from a coworker that was full of inconsistent formulas, missing data, and messy formatting, and I spent hours just trying to make sense of it before I could even start my analysis. Some formulas broke, charts didn’t update, and tracking changes was a nightmare, so how do you all handle cleaning up or organizing complicated spreadsheets efficiently without losing your mind?