A brief should describe and communicate your ideas and intentions clearly.
Information should never be conflicting or contradictory.
Always include a page size, or an artwork size if it is an illustration brief.
If there is a preferred colour palette, font and size, stroke width in mind then please state this!
Remember that things are always open to interpretation.
Sometimes it is handy to state what you DON’T want, it’s just as important as what you DO want.
If you can provide photos, or a sketch to help explain your brief then do so.
A description of the target market: age, sex, race, religion…anything to guide the creative.
If you are handwriting the brief then please make sure the writing is legible.
Here is an example of a really nice clear illustrative brief, followed by the artwork which was produced from it: