Currently the best practice to let users share files can be achieved through the followings:
- Enable Quick Post Type: First you need to make sure you have the quick post type enabled. Currently, files can only be attached to this type of content.
- Create a Topic: You can create a topic2 dedicated to file sharing such as "Docs" or "Templates" or "Files".
- Feature the Topic: You can also feature the topic on the left navigation1 to promote it to users to follow it.
- Highlight the topic within a group: If you want users in different groups to share files as well, you should add the same topic as highlighted topic to a group2 too.