Data cleaning in five steps: from messy to usable

1. Trim spaces and invisible characters with TRIM and CLEAN, or Data → Clean spaces;
2. Remove duplicates: Data → Remove Duplicates, checking the key columns first;
3. Split columns by delimiter or width for combined fields;
4. Normalise formats: DATEVALUE for dates, Text to Columns for numbers stored as text;
5. Handle outliers: highlight them with conditional formatting, then confirm manually.

Advice

Copy the raw data first, and prefer repeatable formulas or steps so next month takes minutes.