W3C has released a draft of Data on the Web Best Practices.
Here's an excerpt:
This document provides best practices related to the publication and usage of data on the Web designed to help support a self-sustaining ecosystem. Data should be discoverable and understandable by humans and machines. Where data is used in some way, whether by the originator of the data or by an external party, such usage should also be discoverable and the efforts of the data publisher recognized. In short, following these best practices will facilitate interaction between publishers and consumers.