Proper data documentation is a necessity, in order to provide context, if you plan to share your data and ideally should be started at the start of the project. Part of this documentation is metadata, or structured information used to describe content and make data easier to find, use, and cite. Metadata records can be embedded into the data or stored separately; different standards for metadata exist among varying fields and subject areas.
While metadata standards differ, it is a safe bet to, at a minimum, include -
See the links below for more comprehensive lists of metadata fields for various disciplines and communities as well as a template for creating a descriptive readme.txt file for your data.
Image by John Norris from Flickr
Some common best practices for data documentation include:
Image by Barry Dahl from Flickr