Sometimes the word governance seems to be overloaded in context of project management. But when it comes to running a country it seems appropriate.

Project governance will:

Outline the relationships between all internal and external groups involved in the project
Describe the proper flow of information regarding the project to all stakeholders
Ensure the appropriate review of issues encountered within each project
Ensure that required approvals and direction for the project is obtained at each appropriate stage of the project.

If I want to implement governance structure in my project,

1) I will create the project organization chart. This will help people understand who is who and what is the hierarchy and escalation points.
2) Details of meetings to be held . Who will join the meetings, what frequency. For eg. there will be steering committee meetings which only Sr. management will join along with PM and there can be technology governance meetings where architects may join.

You must read this wikipedia article on governance, its really good http://en.wikipedia.org/wiki/Project_governance