First of all, the brief helps to create a right communication between brands and influencers. Second of all, the brief is not just a task for influencers, but also an indicator of adequacy. Even if you have the best brand in the world, but you set absolutely boring, inaccurate, stupid or very unspecific task, influencers can simply refuse to cooperate with you. And they'll be right! After all, their goal is to benefit followers and to bring value to your product, and not just to advertise your brand.
And now a few simple rules that will help you to make your brief correct and to attract more influencers, which will unconditionally want to cooperate with you.