Use video first
Videos are more engaging than text or images so use attractive videos in web stories.
Insert more than 6 pages per story it is good practice suggested by Google.
Provide high-quality content
This is one of the most important policies by Google
Keep titles shorter
Make your title in 90 characters. But a good and descriptive title should be shorter than 70 characters
The poster is one of the impotent factors Google recommend to make poster size is at least 640x853px and use an aspect ratio of 3:4.
Make your logo size at least 96x96 px and an aspect ratio of 1:1.
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Make story visible to Google
Avoid using no index tag it will stop your web story to get index
Animation make the story more attractive so use animations in the web story
you have to index your web story sitemap in the search console
Use the amp validator tool
Use the amp validator tool to check your page and story is amp valid or not
These are some factors for best practices for creating web stories for more information go to Google