Advice on Developing an Ops Policies and Procedure Manual

I am working towards developing an operations policy and procedures manual for my organization's Volunteer Engagement Office, but need advice on where to start. During this session, I'd like to review the information I do have pulled together, identify the key sections the manual should include, and receive recommendations on an outline/structure that I can build from.

While I have several components and ideas summarized, they are not complete nor organized into a clear, concise, and comprehensive document. The goal is to develop a document that is easy to follow, so that anyone can step in and get the job done. I want it to also serve as a succession planning tool.