The Open Knowledge Foundation has released The Open Data Handbook.
Here's an excerpt from the announcement:
From a basic introduction of the "what and why" of open data, the Handbook goes on to discuss the practicalities of making data open – the "how". It gives advice on everything from choosing a file format and applying a license, to motivating the community and telling the world. Clear explanations, illustrative examples and technical recommendations make the Handbook suitable for people with all levels of experience, from the absolute beginner to the seasoned open data professional.
The Handbook is divided into short chapters which cover individual aspects of open data. It can be read in a single sitting, or dipped into as a reference work.