PURPOSE Avoiding common mistakes improves accuracy and reduces rework. COMMON MISTAKES Sorting one column instead of full rows, overwriting formulas, mixing data types, hiding important rows, using inconsistent names, and relying on color alone for meaning. PREVENTION Use tables, filters, validation, protected formulas, clear headers, and backup copies. CHECK BEFORE SHARING Review totals, formulas, filters, hidden rows, and permissions. BEST PRACTICE When a spreadsheet becomes mission-critical, document how it works.