Ok you need some spoon feeding it seems. You should have checked the correct answer from the post and searched the key word "SAP Best Practices for Data Migration and Data Quality" in google.
Here's the link SAP Best Practices for Data Migration and Data Quality – SAP Help Portal Page
Also as a heads up, there won't be any single document which gives all the details you need. You need to narrow down your search and focus on the required material only.