When looking at ways to increase performance in an AdWords campaign (text ads or product list ads) reviewing at the incoming search terms is good way to see what is working well and what is not working. To see the search terms go to the campaign or ad group in question and click on the Dimensions tab, drop down the View the box to Search Terms, and select a date range.
Then you can sort by impressions, clicks or conversions to see what people are searching for to find your ads. This is good way to filter through your traffic and increase your return on ad spend (ROAS).
You can also see if your ads are triggering unrelated traffic. For example, if you are selling a Volkswagen Golf and you are seeing search term for golf clubs, this clearly is unrelated search that is unlikely to convert. You can then make a list of keywords by match type and add these to a negative keyword list. This review should be done periodically as new searches come in that could be added to negative keywords for performance optimization.