1. Start small. Small is beautiful.
I believe that an online community should start small. Having thousands of users sign up for your community doesn't necessarily mean many active users. But there's a greater chance for many previously passive users (a.k.a lurkers) to convert into active users if they see that there's already a foundation of leadership and active users who are communicating with each other.
If you reach out to other networks who you think might be interested in your commuinty, your first impression should give them some reasons to come back. Show that there is activity on the site early-on by starting conversations and producing content.
So how do you start small? One way, is to invite a limited set of users to your community, who you trust could provide relevant discussion, content and expertise. These initial users also help to set the tone and direction for the future of your community. After a foundation has been set, the next step is to gradually engage other networks and the smaller niche communities on different websites (Facebook, Myspace, Ning, etc.) who will now be impressed by the activity already taking place in your community.
Examples: Technology forums like slashdot (attract the super nerds first!), online dating communities like okcupid (attract the beauties, or at least those with clear headshots)
2. Develop a thorough understanding of your community's goals.
There is no shortage of "online community building" strategies online. But not all of the pointers out there might apply to your commuity. For example, there are some strategies that are focused on growth or functionalities. But many communities are perfectly happy with a smaller, tight-knit, yet highly dynamic community that focuses on a unique and niche subject. Others might just need more time to develop a foundation.
So before you begin an aggressive marketing campaign, you have to know, "What's important for my community to have?"
Other questions you might want to ask yourself include:
"Does my community need a strong profile-functionality?"
"Does my community need a discussion forum?"
"Does my comunity need a blogging system?"
"Does my community need a rating system?"
By understanding your goals, you can develop the optimal community that matches your needs. Don't just copy the model of other "successful online communities". Too many functions can confuse or overwhelm new users, and dillute the effectiveness of features that DO work.
Examples of fast-growth: Dell, Verizon
Examples of slow-growth: Communities for nonprofits, community groups, student organizations
Example of a low-functionality, yet effective community: Craigslist
3. Allow the community to run itself.
Whether you’re a corporation , small business or a nonprofit, you want community members to be engaged in discussions, sharing expertise or producing content without having to pay anyone. To an extent, you will probably want someone who can be responsible for moderating discussions, checking for abuse, and updating the community, but you want to be able to let others share the spotlight. This will allow the community to run on its own with little-to-none supervision, and develop the community's quality of interaction and content.
Examples: Twitter communities, Yahoo Answers, YouTube
4. Identify the “power users”.
After a while, it’s important to ask, who are the most active members of your site? These are the users you probably want to focus on getting to know because they are the users who are investing time in your community. If you give them your attention and your ears, it is more likely they’ll return the favor. If you’re a large business, your power/super users will offer peer-to-peer support, normally the role of a paid customer service employee. In other cases, your power users will produce the most content and be strong voices and influencers in your community.
However, you might find over time that some users are not actually representative of the needs of most community members. At this point, you have to think about whether you are spending too much time with a user. You should ask yourself, “Does this power user increase the quality of our community or does he/she do more harm?” If a power user is too visible or holds too much influence, they could set the tone of the community in the wrong direction.
5. Recognize top contributors.
Everybody likes recognition for the work they do. It gives people a sense of permanence within the community and a way to make themselves stand out a bit. Communities recognize contributions in different ways; the methods you choose depends on the needs of your community. For example, some sites reward frequent contributors with a "point system" or rankings based on their activity or popularity. Some might provide special site privileges. Some might invite contributors to special events. And some might provide more tangible rewards such as a featured blogger position, or staff role.
By recognizing contributors (however you decide to do it), you're also setting the stage for meeting some of them in person and further increasing the value of the community.
Examples: Yelp, Huffington Post, Slashdot