Quality Score is the number from one to ten that Google shows beside each keyword. It is a diagnostic, a summary of how relevant and useful Google expects your ad and landing page to be for that search. It is not a grade on your account, but it points straight at what to fix.
The three parts
Quality Score reflects three things, each rated as above average, average or below average. Expected click-through rate is how likely people are to click your ad for that keyword. Ad relevance is how closely the ad matches the intent behind the search. Landing page experience is how relevant and usable the page is for someone who clicks.
Why it matters
Google decides which ads appear and in what order using both your bid and its assessment of quality. Ads and pages that are more relevant can win better positions without simply bidding more. Quality Score itself is a simplified view of that assessment, so treat it as a clue about where you are weak, not as a target to chase for its own sake.
Improve expected click-through rate
Write ads that answer the search directly. Put the main keyword and a clear benefit in the headlines. Add a specific call to action. Fill out your assets, such as sitelinks, callouts and call buttons, so the ad takes up more space and gives people more reasons to click. Pause keywords that get impressions but almost no clicks.
Improve ad relevance
Relevance suffers when one ad tries to cover too many different keywords. Group closely related keywords together and write ads specifically for each group. If you offer kitchen and bathroom renovations, give each its own ad group, keywords and ads. Tighter groups make it far easier to match the wording of the search.
Improve landing page experience
Send each ad group to a page about that exact service, not a general homepage. Make sure the page repeats the promise of the ad, loads quickly on phones, is easy to navigate and makes the next step obvious. A page that is slow, generic or hard to use on mobile is the most common reason for a below-average rating.
Improving quality is rarely about one clever trick. It is about making the keyword, the ad and the page say the same thing. That alignment is exactly what we build when we structure a campaign.