As with a comment policy your guest blogging policy should describe what you allow and don't allow in guest blogs. It should define the basis of the relationship between your site and any guest bloggers.
It should also encourage people to submit content and help set up the parameters for submissions. How do you want to receive content? Think about how it would be easiest and quickest for you to publish the content. You don't want to spend hours editing a guest post.
The ultimate goal of your guest blogging policy is to make it as easy as possible for YOU to deal with submissions and to make it easy for guest bloggers to submit quality content.
Below you will find a link to my guest blogging policy. Feel free to use any of it on your own site again :)
I chose the Title: Submit Your Content, as I think it sounds more encouraging then using the word policy :)
God bless...
Shirley