Google published several documents that show the requirements for Google's own products. For example, the Google Developer Documentation Style Guide provides a set of editorial guidelines for anyone writing developer documentation for Google-related projects.

In addition to the documentation guide, Google publishes guides for HTML/CSS, JavaScript and Java.

The guides describe Google's standard for their own content. It's very likely that Google will think that your web pages are high-quality pages if they meet these standards. Here are some key points from the documents:

Recommendations for your content:

• Aim for a voice and tone that's conversational, friendly, and respectful without being overly colloquial or frivolous; a voice that's casual and natural and approachable, not pedantic or pushy. Try to sound like a knowledgeable friend who understands what the reader wants to do.
• Use standard spelling, grammar, punctuation and capitalization. Write short and concise sentences that are easy to understand.
• Use descriptive link texts, i.e. "download the user manual" instead of "click here". If you link to other websites, make sure that these websites are reliable and respectable.
• Avoid buzzwords and technical jargon. Don't use exclamation marks, except in rare really exciting moments.
• Consider numbered lists and bullet lists to structure your content.

Technical recommendations:

• Use tables and lists when appropriate. Only use tables when you have multiple columns of information.
• Use optimized .png files or SVG files with ALT text for images.
• Use HTTPS to embed resources such as images, media files, CSS and scripts on your pages.
• Use HTML to structure your page and use CSS to style your page visually.

"In the official Google blog, Google announced that their local results will be delivered based on the IP address of the searcher from now on. [...]

Typing the relevant ccTLD in your browser will no longer bring you to the various country services. This preference should be managed directly in settings. In addition, at the bottom of the search results page, you can clearly see which country service you are currently using."

"It has become a trend  by SEOs to remove older content, especially older content on a news sites, where sites remove content rather than simply archiving it. [...]

Gary Illyes from Google [...] had an explicit warning – if you remove this older content, you will lose traffic [...] You can redirect that page somewhere, which would be more relevant in your mind, but I typically disagree with that as well, just like you for the same reasons."

"Gary Illyes said the purpose of rolling it out to a limited number of sites is to test it more. The tests seem to be going very well, and it will gradually roll out to more sites over time. He said the rollout will go incredibly slowly, and Google will communicate the process to webmasters along the way.

Google also has a blog post in the works that will be published at some point helping webmasters and SEOs understand the process. The company won’t provide a timeline or ETA for the rollout or the blog post, but Illyes confirms they are on the way."

"We are seeing quite wild swings across all sites. I know there are quite a lot of these predictions around here these days, and yes i do appreciate that updates are happening almost all the time (thank you very much) but this does look like some sort of "larger than a normal day" type update."