The Learning Pool is one of my favourite resources for the use of social media in governmental organisations. Their guides are excellent. I suggest you can download a copy of their latest guide which covers how to use Facebook pages to best effect.
The guide covers the basics like "what is a Facebook page", though to how to get the best use out of one as well as a step by step process to setting one up and marketing it. Huh, wish I'd written this guide myself!