I have been asked several times about community building. For a start, the following points form the basis for any tech community.
Passionate Leader: To build a good community it is essential to have a passionate leader with strong temperament. The leader must be duly motivated, ready to accept suggestions and advise accordingly. The leader must also be ready to help members, motivate others and stay positive throughout. With a strong temperament like this, I would say half of your work is done.
Coordination: Every member of the team should be aware and coordinate with other members to comprehend the happenings of the project. Members should have equal say in the product development under a democratic process if available.
Contribution/Documentation/guidelines: Good documentation will result in easy user base creation. It will also motivate a lot of these users to turn into collaborators. Hence it is always suggested to provide easy, clear and crisp contribution including some quick screencast.