Structure first.
WHAT TO SEPARATE
Raw data, on its own sheet Calculations, on another Output and charts, on another
WHY
Mixing them makes the file fragile and impossible to update.
WHAT THE DATA SHEET SHOULD CONTAIN
Headers in the first row One record per row No blank rows No totals No formatting carrying meaning
WHAT TO FREEZE
The header row, so it stays visible.
WHAT TO NAME
Every sheet, meaningfully.
WHAT TO DOCUMENT
On a notes sheet: where the data came from, what was cleaned, what each calculation does.
WHY
In three months you will not remember.
WHAT TO AVOID
Calculations scattered across the data Hidden rows and columns holding working Several people editing one file simultaneously without control
WHAT TO PROTECT
Formula cells, so they are not overwritten accidentally.
WHAT TO TEST
That adding new rows updates the summaries.
If not, the structure is wrong.
