Hopefully, you've already created this by now, so you'd have many more pointers to add than I present here. But since this thread has resurfaced and I've done a lot of these, I thought I'd just add some extra things that others may find useful. I've created several handbooks for previous jobs and they stayed in use for training long after I'd moved on. Caveat: I've never done one for theater, except for my own personal notes. Also, my previous responsibilities were for building/starting new teams, whereas you may have a team already in existence.
1. It always helped me to start with an outline first, including things like: processes, policies, forms, contacts, etc. This outline becomes the table of contents. For processes, I would draft each section roughly, and refine as I went through the process myself.
2. I also start with big picture/contextual orientation first to help them get the lay of the land, which included some team history, mission/vision, larger goals (in this case, it might be a season schedule), how the department fits into the company. For anyone working with other departments, contact lists (and *why* to contact them) are critical. Navigating the organization is the first step to getting comfortable with a job.
3. I think it is important for people to have both a 50,000 ft view of their job as well as the 100 ft view, so I would include an overview about what the SM's core responsibilities are. Also, cheat sheets are great (one-pagers about the most important things, and then you can include detail elsewhere).
4. If your company doesn't already provide a general handbook, you may want to outline specific office tasks, like how to use the printer/copier or how to login to a web app - just basic productivity in another section. (If you can address it by an office tour, do that). Get into specifics once they have their bearings. If someone from outside of the company is taking over for you, this is super important because knowing these little office things will affect their ability to get off the ground. If it will always be someone from within, they'll probably already know these things, so you won't need to provide that. I would err on the side of caution though. You never know when they'll need to get someone from the outside, and that's much more likely to happen with theater than it was in the corporate world.
5. Maybe a philosophical issue, but I am not very draconian about forms (personal preference - I also don't like telling people how to do their jobs as long as the results are right). I include them as examples or resources. People will usually use the forms you give them anyway, and I think a little deviation allows for some flexibility, freshness, and evolution. Since they will be in a decision-making position, it may help to let them know how much they can deviate from the manual; that may depend on the culture/age of the company. In my corporate life, we were very liberal which allowed for some great invention. Sometimes the wheel did get re-invented and sometimes the wheel was improved. But it helped us learn what was "best" and see different ways of working.
6. Try to keep it short, because it will grow and you want people to get started quickly.
7. For anything requiring complicated computer navigation/new software, people *love* screenshots.
8. To get people up to speed, the manager also provided them with a personalized "Getting Started" doc, so that they knew what their first projects were going to be, which meetings they needed to attend, distribution lists and who to include on notes, who they needed to start talking to, how to navigate the fileshares, what documents would be helpful to read and where to find them, etc. so that they could be an involved team member as soon as they started. (Unlike #2, this is a section related specifically to the department). Knowing who/how/when they need to interact with was key. For your project, I would have a section that is a timeline-styled procedural doc that other posters have mentioned. Basically something that very specifically says, "These are the pieces of your job. Do this."
9. ... which brings me to Checklists. Who doesn't love checklists? For this project, I'd use a lot of that format because you want whoever does your job to hit the ground running without missing a beat.
10. I also want to keep the information only in one place because it's easier to maintain only one section if it changes. I will then reference (via link) that section as needed. Resist the temptation to copy/paste information.
11. My favorite part of creating handbooks is the hand-off, when the first person who is going to use this gets it and they become the "owner" of it. They become responsible for adding anything they would have found useful, or anything that has changed. I hate maintaining handbooks, but it is a great first assignment for someone new and it gives them something very useful to do. Especially because they are the final audience. Since they just read it, they know exactly what they would improve about it!
12. Especially if it's a close-knit team or a training doc, I often have a section where they can pass on a few words to their peers at the end of the handbook - something that conveys culture and voice. Sometimes this becomes a functional "best practices" section, or a "what to do if...", or just a humorous selection of quotes. Often this ends up relaying something about the culture or values of the organization (for example, "a short, fast response is often better than one after 2 weeks of research", "Use spellcheck.")
13. Finally, I don't see the handbook as ever finished. If it's useful, it will be a living, breathing object that evolves as work processes of the organization does, even long after you've moved on. It is important to me that other people also own it and can update it as necessary. I would opt to use some sort of collaborative software, preferably one that tracks authorship and dates. (In my previous life, we used wikis... but this is theater we're talking about!)
