The summary.
THE MOST VALUABLE FIELD YOU CAN ADD
How each enquiry or customer found you.
It answers where business actually comes from, which most owners guess wrongly.
THE SECOND MOST VALUABLE
What each sale cost you. Without it, profitability is unanswerable.
THE RULE FOR STRUCTURE
One row per record, one column per attribute, one value per cell.
Merged cells, totals inside the data, and colour used to convey meaning all break analysis.
CONSISTENCY DECIDES ACCURACY
Three spellings of one customer become three customers.
Agree how things are written, provide selection lists rather than free typing, and check unique values periodically.
ALWAYS WORK ON A COPY
Keep the raw export unmodified, and record what you cleaned and why.
CHECK EVERY EXPORT AGAINST THE SOURCE TOTALS
Exports are frequently filtered in ways you did not expect, and spreadsheets silently mangle dates, leading zeros and long reference numbers.
WHEN COMBINING SOURCES
Check how many records failed to match. That is the check people skip and the one that reveals the problem.
BUILD IT MANUALLY BEFORE AUTOMATING
Automating something wrong produces wrong answers faster.
