There's a fantastic article on Wired called "Web 2.0: A Pattern Library" written by Tim Ziegler. The article provides a great summary of best practices and principles that are floating around; and covers everything from content management and information architecture to human filtering and "folksonomies".

Especially important is the notion of iterative development of web campaigns. Todays tools provide an unprecedented level of flexibility and agility that allow marketers to make frequent changes and receive feedback in near real-time.