A bad brief costs more than the time spent writing a good one. When a client hands over a vague brief, the agency spends weeks asking clarifying questions, proposing strategies that get rejected, and reworking plans. The client interprets this as the agency being incompetent. The agency interprets it as the client not knowing what they want. Both may be right.
What to include in a good brief
Start with the business context, not the marketing ask. What does the business do, who does it serve, and what is the commercial goal for the next 12 months. Revenue target, deal count, market share — pick one and be specific. "Grow the business" is not a goal.
Then state the problem clearly. Not "we need more leads" but "we generate 40 inbound leads a month, our sales team says they need 80 to hit target, and our current cost per lead is £180." Numbers are not always available, but estimates with reasoning are far more useful than vague descriptions.
Include your constraints. Budget, timeline, internal resource, channels you have already tried and why they did not work. Agencies will work around constraints they know about. Constraints they discover mid-engagement cause delays and resentment.
Define what success looks like at three months and twelve months. If you cannot define this, neither you nor the agency will know whether the engagement is working.
What to leave out
Do not specify the tactics. If you tell an agency to run LinkedIn ads, you have already made a strategic decision without the benefit of their analysis. Brief the outcome, not the method. If LinkedIn is the right answer, a competent agency will tell you. If it is not, you want to know that before you spend the budget.
Do not include competitive analysis unless it is based on actual data. Assumptions about competitors tend to send agencies in the wrong direction.
The question most clients never answer
What does your best current customer look like, and how did they find you. Not your target customer — your actual best customer. This single piece of information tells an agency more about where to focus than most briefs contain in total. If you do not know the answer, find out before you brief anyone.
When you are not ready to brief an agency
If you do not have a clear sense of the business goal the marketing needs to support, you are not ready. Agencies can help you refine a goal, but they cannot define it for you. And if the decision-maker will not be involved in regular reviews, the engagement will drift — no matter how good the brief was at the start.