There are 2 types of resources to learn Seach Engine Optimization (SEO): the official resources and the notorious resources.
1. The official resources
- Google Search Central.
- The Search Quality Rater Guidelines (Overview) and the Search Quality Rater Program Guidelines.
- Bing Webmaster guidelines.
The Twiter accounts
2. The notorious resources
3. My comments
Knowing SEO is about knowing the trinity of a search engine:
- Serving (ranking)
If your read carefully the resources listed above, especially the documentation section of Google Search Central content, you can safely call yourself an SEO expert.
SEO is about performing 3 tasks, and 3 tasks only:
- Implement technical SEO requirements or features on your website.
- Create and publish quality content on your website.
- Promote your content (in order to get backlinks).
The work of an SEO expert or consultant is related to these 3 tasks. There is nothing else to it. But doing tasks 2 and 3 consistently is hard.
In this list, there is a document which is quite different from the others. It is the Search Quality Rater Program Guidelines. I invite you to read the following article to understand the paramount importance of this particular document: A machine learning engineer's view on winning at SEO.
Google doesn't communicate a lot about their search engine, which is normal. From time to time, they might address particular issues that is brought to them, with specific videos or specific articles on their blogs, but the general rule is no comment, stick to our guidelines and everything will be fine. However, they usually do have an official spokeperson who is in charge of communicating about publisher and webmaster issues, online and in conferences. From 2005 to 2015, it was Matt Cutts, head of the Web Spam Team. Since September 2017, it is Danny Sullivan, who is the first "Google Search Liaison".
There is nothing really new in the notorious resources compared to the official resources. But you will find more examples and concrete extrapolations of the official recommendations.