This document goes into to detail about what is a policy brief and how to best write one. There is probably more information here than you need, but since policy briefs aren't a format you often encounter this article will help get you started.
This article from Nature is meant for non-scientists reading policy that contains scientific claims. It will help give you an idea of the audience for policy, what they are looking for, and how they are interpreting the science within a policy.
This article was written in response to the Nature article above. It is written by policymakers to scientists letting them know things they should consider when communicating with policymakers and writing policy briefs.
"Nearly every major issue facing society has science at its core, including economic productivity, healthcare, and climate change. Science and scientists can play an important role in informing decision-making on these issues. This workshop offers an overview of the science policy landscape, strategies for effectively engaging policy makers, and the role of science in the policy process."