Start with the right checks.
Migration Assistant can help bring information to a replacement Mac, but you still need to check applications and account ownership afterward.
What to do next.
Inventory important files, applications and external drives. Confirm the intended owner of each account.
Follow Apple’s preparation instructions and confirm that the new Mac has sufficient storage.
If the new Mac is already set up, open Applications > Utilities > Migration Assistant. Otherwise use the transfer option during initial setup. Choose the source Mac or Time Machine backup and review what will be transferred.
Allow the transfer to finish, then sign in to the intended account on the new Mac.
Check the result.
Open recent files, check important applications and verify shared workspaces. Keep the old machine unchanged while missing items are investigated.
Stop and get help if…
A transfer would merge unrelated business and personal accounts, an application requires specialist data movement or a backup cannot be read. Do not erase the old Mac to finish the handover faster.