I just created this for a training I am doing at Comcast later today.  I wrote it with Linkedin in mind, but it should do well for many other social networking sites like, hmm, I don't know, maybe this one   I hope it helps.  Better yet, what would you add to it?

Social Networking Profile Guidelines

IF you decide to put up a profile on Linkedin.com, Motorcityconnect.com or other sites, make sure you do the following:

• Fill it out completely
• Make it easy and enjoyable to read
• Use Keywords that are relevant to your business
• Add your college/university (if applicable)
• Give people a reason to connect with you
• Be clear on how they can help you
• Demonstrate yourself as an expert
• List hobbies and other activities
• Make it uniquely yours
• Post a picture

Use the summary section to talk who you are, not what you do. You will have space to talk about that under experience. The summary could talk about your business philosophy, why you do what you do or why you are on the site and with whom you hope to connect.

A good example for your current position as a sales rep at Comcast:

I'm a business development professional at Comcast. I help companies improve efficiency and productive while lowering operating cost. We provide ridiculously fast access to the Internet and have outstanding rates on telephone service. Our clients thank us because we are the best alternative business communications provider there is.

It's up to you as to whether or not to add previous employment on your profile. Remember, you are there to connect with people. Solid connections start with common ground. Sharing a previous employer is as common as it gets.

If you do decide to join any group, be active. Find out how to become a leader in the organization. Leaders get recognized. Remember, it's not who you know, it's how you're known.