Purging Dead Keywords From Your Campaigns
With keywords and ad groups that number in the thousands, it can be easy to forget about some of the longer-tail phrases that aren't performing at all. But Frederiksen notes that having an abundance of 0% CTR keywords in your account can actually cause the platform to lower Quality Scores across multiple campaigns.
He recommends searching for these hidden quality-killers every three months or so, and purging any keywords that haven't garnered a single click. It may be hard to let go of some long-tail terms (for fear of losing those few perfectly matched searches), but eliminating them will likely lower your bids and bump up your Ads Quality scores--and even create space for you to test out different terms.