Split ad groups that have a high number of keywords into smaller and more tightly themed ad groups. Make sure the ad text reflects the keyword theme of the ad group. The best way to do it is to place the keyword in the ad text.

Ensure that the landing page is relevant to the ad.

Make sure the bids for the keywords in the ad group are competitive so that the keywords and ads get a chance to show. 

On the "Account Summary" page, you’ll notice the Quality Score at an overall account level. While, in the tree view on the left, campaigns are color-coded by Quality Score and segregated accordingly. Dark and light green indicates a high Quality Score, Yellow is medium, and Red is the lowest.

When you see a campaign with a red mark, it means it has a low Quality Score. Click on the campaign name to know more about the keywords and ad groups that are causing it.

Identify campaigns that have a low Quality Score and need immediate attention from the Campaigns tab in the Quality Score Tracker. Use the campaign level Quality Score along with cost data to prioritize these campaigns.

Find out which ad groups in the campaign are bringing down the overall campaign level Quality Score.

Optimize the ad group to improve ad text to keyword relevance which will help increase the clickthrough rate (CTR) and eventually Quality Score. A high Quality Score usually means a low average CPC.