Kingsley used this line in a Forrester Webinar today titled "Creating Successful Customer Communities," and I thought it mades a lot of sense.

When talking to people about online community they often ask, "Is there a way to start small and grow it over time?"

The tone of your community is set very early, and as they say you don't get a second chance to make a first impression. If it feels vibrant and full of activity, then your visitors might be inclined to post a comment or bookmark it. So what makes a community vibrant?

• No matter what the size, make sure you seed it with 10 ideas to kick things off.
• A good looking UI goes a long way towards helping people buying into the vision.  
• Typically the bigger the audience the better. If you invited 1,000 people to your community might get 40 ideas a month. A community which is generating 2 new ideas a day is more interesting than one that generates 1 a month. 
• As much as possible concentrate your community. Salesforce offers multi-site administration but it is often better to create a new category vs. creating a new community. 
• If at all possible go external. You typically have a better audience when you open it up to customers and partners. You can also open up a line of communication for a disenfranchised group who can't wait to be heard. 
• Public sites are the way to go if you can. It's much easier to drive awareness and people are more likely to link you to. You also get picked up in search creating inbound referrals.
• The more images you can use on your site the better.
• Join the conversation. Use the moderator icons and let people know you're there. Commend them on their good ideas and let you know you appreciate the feedback. You can also ask question in the comment stream and let them know when something's being delivered. 
• Create Dashboards to measure success. You're going to want to see the # of register users, logins, posts, votes, comments, and ideas by status to throw out a couple metric you might want to track.

I'm sure there are a bunch of other great best practices for creating a vibrant community. If you have one, post it as a comment below.