Google AdWords Clickthrough Rate

Keep a close eye on keyword performance with these strategies:

• Update your keyword lists regularly. Pause or remove the words that aren't working well for you (for example, if they have CTRs below 1%, or low Quality Scores) and add new ones. Add columns and segments to your statistics table on your Keywords tab for an overview of your keywords' clicks, CTR, Quality Scores, and more.
• Use the four keyword matching options to help control who sees your ads. Add the Match type column to the statistics table on your Keywords tab to see how the different keyword matching options perform for you. With some options, you'll enjoy more ad impressions, clicks, and conversions. With others, you'll get fewer impressions and more narrow targeting.
• For a comprehensive view of keyword quality, run a keyword diagnosis. It gives you information about your keywords' Quality Scores and whether they're triggering your ads. A Quality Score of 5 or higher is generally considered good.

https://support.google.com/adwords/answer/1722035