The following are the strategies and tactics that managers in organizations have reported using for improving community metrics:

• Engagement by Hosts: Being an active participant in your own community.
  Contribute to conversations, praise exceptional users and content. Be “present” in the
  community.
• Marketing Externally: Reach out to blogs in your space, make sure your site is
  optimized for search, mention your community via your other marketing channels.

• Marketing Internally: Educate new users on community feature set. Place prominent

calls to action to participate. Create email vehicles to send “best of the best” content
and encourage members to visit the community. Make it easy for members to refer
other members.

• Leaders: Find and/or cultivate community members that can act as your evangelists,
  community greeters, and second-tier moderators.
• Site Experience: Ensure that the site experience is a quality one. Conduct ongoing
  satisfaction surveys and usability test. Ensure site performance is optimal.

Source: Online Forum Communications