Decide what to move
List customers, contacts, products, open orders and any history needed for daily work. Identify duplicates, inactive records and data that can stay in a read-only archive. Agree who can decide when source values conflict.
Example: importing company records
For each source field, record the destination field and transformation. For example, split a combined address into the required parts and preserve the old company identifier for matching. Define what happens when a tax identifier is missing or two rows represent the same company. Try these cases on a small sample.
Compare the result with the source
Check counts, relationships and selected business totals. Open sample records with users. Keep rejected rows and their reasons so they can be corrected and retried. A successful import response alone does not show that all the data is correct.
Plan the last transfer and a return path
Agree when changes stop in the old system, how the final differences are imported and who approves the result. Set the conditions for returning to the previous system. Rehearse that return, including any data created after the switch.