Guidelines nobody opens
Almost every company we start work with has a set of brand guidelines. Almost none of them has opened it since the handover meeting. The document is usually good. That is what makes this interesting.
The version we are handed is typically eighty to a hundred and twenty pages, properly typeset, with a considered cover and a contents page. Somebody was paid well to make it and did a careful job. It covers the mark, the clear space, the colour values in four systems, the typographic scale, the photographic direction, and a page near the back about tone of voice with three adjectives on it.
And it sits, unopened, while the marketing team invents its own answers in Slack.

What a guideline is for
The reflex explanation is length. Make it shorter, people say, and they will read it. We tried that for about two years and it does not work, because a shorter document organised the same way is a shorter document nobody opens.
The actual problem is structural. Guidelines are almost always organised by discipline — a colour section, a type section, a photography section — because that is how the studio that made them worked. But nobody arrives at a guidelines document wanting to know about colour. They arrive because it is Tuesday and they have a specific problem: the mark has to go on a photograph and the photograph is busy, or there is a form to build and nothing says what a required-field asterisk looks like, or a sales deck needs a chart and there is no chart style.
A document organised by discipline cannot be searched by someone holding a question. They have to already know which section their problem belongs to, which is exactly the expertise they do not have.
A guideline that documents a decision is an archive. A guideline that answers a question is a tool.
The other failure is subtler and harder to admit, because it flatters the studio. Guidelines get written to record what was decided, and deciding is the fun part. The interesting document to write is the one that shows the reasoning, the routes not taken, the logic of the system. The interesting document to use is the one that says: here is the thing you are about to do, here is what to do, here is the file.
Those are different documents. Most studios write the first one and hand it over as though it were the second.
What to write instead
We organise ours by question, and we get the questions by asking. In week eight of every project we sit with the people who will actually use the system — not the person who commissioned it — and ask what they made last month. Not what they might make. What they made.
The list comes back remarkably consistent across sectors: a slide, a social post, a form, a signature, a document template, a name badge, a sign, an email. About fifteen things, and they account for nearly everything a brand is asked to do in its first year.
So the guidance covers those fifteen, in order of how often they happen, each one answered in a page or less with the file attached. Then, at the back, the reasoning — because somebody eventually needs it, usually the next studio.

This produces a shorter document, but shortness is a side effect rather than the goal. Ours run twenty to thirty pages, and the reason they are that length is that fifteen answers do not take a hundred.
Ours are shorter than yours and they get opened, which is the only measurement that matters.
The test we use is blunt and it is the only one we trust: hand the document to somebody who was not in the room, give them a real task, and watch. If they open it, find the answer and stop reading, it works. If they open it, scroll, and then ask a person instead, it does not — and no amount of typographic care will change that, because the failure happened at the contents page.