Here some simple tips that have worked for others who searched for policy:
Just want longer reports, no blog posts? Add filetype:pdf to your search. This typically will return reports. Toggle for "Date" on the top right, and you will get the most recent reports.
Want to exclude Brookings? Add -brookings.edu to your search. Similar exclusion works for other institutions or individuals.
Entirely new to a policy field? Run a broad search, and find two or three key terms that allow you to do a more focused second search.
Let us know whether you find any particular challenges.