What to consider

Plan how old data will be mapped onto the new SharePoint system. Legacy systems often have a large number of free text fields and unmanaged folder structures. Migration offers a golden opportunity to ensure the new structure is better and more effective. This will involve setting up governance policies for how documents are stored and defining new metadata and taxonomy.
To ensure success, you should do the following:

Define the destination format, metadata and policies in SharePoint.


Understand the structure of the source system from which you are migrating.


Identify where data may be unclean or missing and define an approach to address this.


Map old metadata fields to the new metadata fields – omitting some, introducing new ones as needed and providing translation tables.