While he focuses on communities formed around commercial products, his advice is generalizable to other types of communities:

1) Create something worth building a community around
If you dont have something that people can get excited about, they wont form a  community around it.

2) Identify and recruit your thunderlizards-immediately!
Find people who are enthusiastic about your product or service and recruit them to start the community

3) Assign one person the task of building a community
Make it someone's top priority and full-time job to champion and lead the community

4) Give people something concrete to chew on
Make your product customizable, and extensible

5) Create an open system
Give people the tools and information they need to tweak, customize, and build upon your product

6) Welcome criticism
Celebrate criticism and feedback, and be responsive to it

7) Foster discourse
Provide a platform for communicating ideas and opinions, and be engaged in the conversation

8) Publicize the existence of the community
Make it an integral part of your sales and marketing efforts.