Most creative projects that go wrong do not go wrong in the design. They go wrong in the first conversation, because the brief never said what the work was for. A brief that works is short, but it answers four questions.
1. What is this for?
State the outcome in one sentence. "More enquiries from small business owners" is an objective. "A nicer looking homepage" is a task. When the objective is written down, it becomes possible to tell whether a design decision is helping or just decorating.
2. Who is it for?
Describe the person, not the demographic. What do they already believe about businesses like yours? What have they tried that did not work? A single paragraph of genuine detail is worth more than a page of age brackets.
3. What already exists?
Send whatever you have, even the parts you dislike. Existing logos, old copy, competitor pages you admire, that one photo everyone uses. Knowing what you do not want is as useful as knowing what you do.
4. Who decides?
Name one person who can approve the work. Projects stall when feedback arrives from four directions with equal weight. If several people need to be heard, agree in advance that one of them consolidates the feedback into a single written round.
What a brief does not need
It does not need a colour preference, a font suggestion or a reference to a website you saw once. Those belong in the conversation after the objective is agreed, where they can be tested against the purpose instead of driving it.
If you only have half of this written down, send the half you have. It is far easier to fill a gap than to unpick a decision that was made before the objective was clear.