According to Search Engine Roundtable at the Google Groups, the Google AdWords Pro, Sarah has stated some criteria that should be kept in mind, if you are looking for good Google AdWords quality score.

The critical factors are:

1. CTR: The higher, the better.
2. Account structure: Your keywords should be in "tightly themed ad groups."
3. Landing Page Quality.
4. Account history: Your average CTR.

Historical CTR of the display URLs in the ad group.

Here are a few excerpts from that thread at Google Groups:

"Can you throw some light on the various factors that affect the
quality score that you've come to know through experience?

"Hi Ekalaivan!

There are six main factors that help determine quality score.

1. Click Through Rate (CTR). On a personal note, I think this is the most important because it really shows users' interest in your ad. At the end of the day, you want people to click on your ad and Google wants to show ads that are useful to the user. A high CTR is a great indicator that the ad is relevant and of interest to users searching
   on a given query.
2. The Structure of the Account. Make sure all of your keywords are in tightly themed ad groups. This relates back to #1 because you want to make sure that your keywords trigger a relevant ad. Say for example, you had the keywords 'cookie gifts' 'cookie gift basket' 'cookie
   baskets' and 'cake delivery' in one ad group. Since all of these keywords will trigger the same ad text, it would be tricky to write a headline that encompassed both 'cookie gifts' and 'cake delivery.' If you break 'cake delivery' out into its own ad group, you can write a targeted ad text that will help increase your CTR.
3. Landing Page Quality. In a nutshell, make your site the best it can
   be. (For more specific tips, please see https://adwords.google.com/support/bin/topic.py?topic=9356)
4. Your Account History. This is measured by averaging the CTR of all of the keywords and ads in your account. (Tip: If you have keywords with some impressions but no click (0%CTR), delete or pause them to improve account quality).
5. The historical CTR of the display URLs in the ad group.
6. Other relevance factors.*

* I recognize this could be hundreds of other factors, but in my
experience, if you focus on the top five, you should be fine.

AdWordsPro Sarah "

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