XmlCodingTechniques is a page dedicated to using Xml in the best ways for the task on hand.
The assumption is that a decision has already been taken to use a XML related tool, or use Xml as a transport, etc
XmlNameSpace related links
XmlSchema best practices Feb2003 http://www.xfront.com/BestPracticesHomepage.html
General Resources
See also a book called XmlElementsOfStyle