PURPOSE Cleaning data makes spreadsheets easier to analyze, import, and trust. COMMON CLEANUP TASKS Remove duplicates, trim extra spaces, standardize capitalization, fix date formats, split combined fields, and remove blank rows. WORK SAFELY Make a copy before cleaning. Use filters and helper columns instead of destructive edits when possible. CHECK RESULTS Compare row counts, totals, and samples before and after cleaning. BEST PRACTICE Document major cleanup steps so others understand what changed.