There are three elements of the quality score.
The biggest one is click through rate (CTR). Google highly relay on customer feedbacks to decide which Ads is the best for each search query.
Second important is Relevancy. Google determines the relevancy by analyse the language in the context in the ads and query to determine how well related to keywords.
Third, the landing page quality. It is the most ignored element by many of us. A high quality landing page is the combination of relevant information the user is looking for, easy navigation, original content, quick landing time, minimum pop ups, transparent about the nature of your business. If your bounce rate is high, you need analyze the landing pages of each ads.
Do not forget what decide your Ads rank is not only one parameter.
Rank= Max Bid X Quality Score
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