Implement data classification by defining organizational data categories, such as public data, confidential data, etc. Automated tools to label files, per their sensitivity levels, may be used. Appropriate security measures/protection should be implemented, per its categorization.
Use data classification, tagging, or metadata fields based on industry-standard frameworks such as (but not limited to):
a. Carnegie Mellon University: Guidelines for Data Classification
b. SANS Institute: Tagging Data to Prevent Data Leakage (Forming Content Repositories)
Classify data according to its type and sensitivity level.