‘Give me the freedom of a tight brief’ – it’s a call from writers across the world.
The more you have nailed down your idea into a coherent brief, the more you’re going to get out of your writer. Rather than telling them exactly what to write, give them signposts – information which lets them research and make the piece their own.
Include a line or two on what you want the reader to feel, on how this topic fits with the client’s offering, and what action you want this piece to drive.
If there are ‘must include’ points (perhaps provided by the client) or SEO considerations, keep these in a separate table on the brief document.
And if you have extensive views on structure, create a separate (but short) document. Let the actual brief itself flow like a good piece of writing – your writers are readers too. Be kind to them.