Create a mapping document containing these three parts:
Filename-pattern
Info/photograph/artwork template mapping
“Types of categories” mapping
Example: (mapping document)

1. Construct a layout for the filenames of the media files according to the pattern: “<short description>_-_<institution>_-_<id>.<ext>”. <short description> should be a meaningful description of what the file depicts, to make easy reuse possible as it is more easy to search for.
2. Determine which metadata field(s) make up <short description>, and any needed conversions of these (e.g. combine multiple fields, trim text endings).
3. Determine which metadata field(s) can make up the <id> part (which ensures unique filenames). If no metadata field fits, make up your own method for assigning unique ids, e.g. 1, 2, 3.

See also official guideline for filenames on Commons.

2. Decide on the main Commons information template used to carry the information on the Commons file description page. The choice is normally between one of Information, Artwork or Photography, but there might be better alternatives for specialised collections. Different templates might also be used for different sub-sets of the batch. Avoid creating your own new information templates.
3. Infobox was selected after internal deliberations

3. Map metadata fields to parameters in Commons template. Make it clear which metadata is used where in the selected template, how they must be transformed etc.
4. Determine any needed conversions (e.g. of dates, parts of strings etc).
5. Determine any implicit values (e.g. OTRS, Licenses, collection theme).
6. Determine any fields needing mapping lists.
7. Consider possible Wikidata connections.

4. Determine metadata fields which can be used as basis for categorisation (possibly via mapping lists).