Join groups within the social networks where people you know are likely to hang out. In my opinion, the reason that LinkedIn and Facebook haven’t become unmanageable as they’ve gotten bigger, is that they’ve encouraged the development of small groups where people can talk about shared interests. Increase your credibility and visibility by using your professional expertise to add to these discussions.
Post frequently, but judiciously. Meryl’s comments about Twitter overload applies to the social networks as well. I’ll also add that services allowing one to post simultaneously to multiple networks, such as Ping.fm, are great, but should be used carefully. The networks have different audience demographics, and this should be kept in mind when you’re deciding what and where to post.
Use the networks’ automated tools for finding people you know. The networks can, with your permission, review your address book and see who you know who’s already on their network. They also have a “people you may know” function that recommends possible contacts. LinkedIn’s system has worked well for me; Facebook’s seems to be less accurate. The recommendations presented to you are based on background data (schools attended, former jobs) you provide to the networks, so it’s worth the time to provide complete information in your profiles — assuming you are comfortable with their privacy policies.
Use RSS feeds to follow what the members of your network are doing. The folks who run the social networks want you to visit their web sites, of course, but I find it more convenient to follow the activity of my connections through an RSS reader.
Add your Facebook instant message account to your IM program. Facebook’s instant message system can be added to multi-protocol IM programs. On my Mac, I prefer Adium; the PC users in my company like Pidgin or Digsby.
Use privacy settings to minimize email notifications. For Facebook, the AllFacebook blog has an excellent privacy primer; note, though, that Facebook is in the process of updating its privacy settings. And check out PC World’s discussion of privacy settings for LinkedIn. You’ll want to use these settings to control how and when the social networks email you. I find that since I follow the networks’ RSS feeds, I can turn off most of their emails.