First, you need to understand how ads fit in the process of the searcher behavior funnel. A searcher expects to see a site (in the natural results) or an ad that is relevant to their search query. The more relevant the ad is, the better.
Once they click on your ad, you need to take them to a relevant landing page that contains rich content, including the searchers query and elements of the ad copy — especially any promises you made.
This sets the proper expectation for the searcher, and is more likely to result in an action, which translates to a higher CTR and higher conversions. These factors, along with relevant ad copy and relevant landing pages, will increase your quality score. The benefits of a higher quality score are better keyword ranking and lower CPC.