Who is this runbook for?
Write better runbooks by building a mental audience so you know what to include, and what not to.
As with any good writing, one of the most important things in writing a good runbook is to figure out: who is it for? In the case of a runbook, this is the same as answering: "Who is going to do the work in this runbook?" The problem with writing a runbook is that they are frequently used by multiple people with wildly different needs. So, how do you answer the question?
Keep a Specific Person in Mind
The easiest way to keep the proper perspective in mind is to pick a few people who represent the different audiences for your runbook. In fact, think of specific individuals whom you know well, and whom you've worked with for a little while. That way, it will be easier to put yourself inside their head while you're writing your runbook.
Generally, you can include yourself as an example of an expert who is also familiar with your business. However, you have to assume you're writing for your future self who's been away from this task for few weeks or months, and needs a bit of reminding. As you're writing the titles for each step, ask yourself: "What would my future self need to remember how to do this?" Your future self will, of course, not require a lot of detailed hand-holding. You just need a set of crisp, short instructions to jog your memory.
The New Guy
The second person you want to think of is the most recent experienced person to join your team. They are generally experienced in their field, but they don't know your systems yet. When writing the descriptions of each step, try to recall what you did and didn't need to tell this person when getting them started. What do you already know is unique to your business? What seemed surprising to them which they hadn't seen elsewhere? What tools or software had they not used before? On the other hand, what was already obvious to them? All of these will help you decide both what to include and what not to include.
A third person you might want to include in your mental audience is the last person you hired with no background at all (e.g., an intern or new grad). What terms, acronyms, or concepts tripped them up? What questions did they have which your "experienced" hire didn't ask? On the other hand, what kinds of things seemed to be general knowledge they already had? You may not want to actually spell all this out in your runbook—it is meant to be a working document: not a tutorial—but you might want to include links to other materials to help novices figure things out.
The Special Cases
Between these three people, you're usually pretty well covered. However, if your runbook involves working with computers (or some other specialized skill), you might include both someone who's very good with computers, and someone else who is bad with them. Or, if your runbook involves different people handling different steps, you will want to include an example of each. If you know this task got botched in the past, think of the person responsible, and try to figure out what you could include which would have prevented the problem.
Our product, Runbooks, is specifically designed to make this approach to perspective-taking as easy as possible. Not only does each step allow a separate title and description, but they all live online in a shared location, so it's easy to actually ask your different audience members for feedback.