If you are running display campaigns, you should periodically review performance on specific placements to ensure that your ads are shown on quality pages that meet your goals. This is especially important if you are running keyword-based, interest- or topic-targeted campaigns, where AdWords places your ads on pages you may not have chosen. If your ads are shown on low-quality placements, or placements that generate clicks without any conversions, you can exclude them in AdWords and block such websites from displaying your ads.
Before you start excluding specific placements, review their performance. Specifically, pay attention to the following:
High-cost placements that generated zero conversions.
High CPA placements.
Low-quality or irrelevant placements.
Placements with high bounce rates and low time on site. You will need to access your Google Analytics to find this data.