I think there are a couple types of guidelines that are useful:
Procedures – what are the processes/guidelines to participate in social media in my agency? Do I need approvals? Where do I go for them?
Best Practices – how do I do this well? What works on social media for government? What types of content and questions, etc? Tips, tricks, etc
Why it is important – what is the business case to help me sell this in my division?