I just read a great post on Social Networking Best Practices on Smashing Magazine. The article discusses the top 10 on ways to ensure your social network is the best it can be. Everyone should take advantage of the author's simple tips. (As a side note, it amazes me how many organizations are not following these simple rules. The easiest way to ensure product failure it to make the network hard to use and engage with other users. Why not set your site up for success from the get go?)
To her list I would also add:
The user should be able to see discussion topics and treads with ease. There should be a structural hierarchy and a clear organizational method i.e. sort by topic or topic groups, see the most recent discussion, and so on.
Engagement - Expanded
If you tell users how many new users join your network and the number of new groups that have been created allow them to SEE these users and groups. Telling them that new things exist does nothing if they can't utilize the information in some manner. Engagement with other users needs to be effortless and take a minimal number of clicks.
Applications - Be Wary
We all admit it was fun to throw sheep at people in the beginning of the "application movement" in Facebook. Be wary of adding too many applications that take the user away from the original attended purpose.