But here's is a list of some essential optimization methods and practices we use. That list is being constantly updated and is platform dependent. Each method mentioned has it's own logic and approach.
Secure HTTPS / SSL website loading ( provide valid Secure Socket Layer Certificate )
Incorporate multiple website navigation - Top, or main navigation, for functional elements, and Side navigation ( example ) for categorising content
Include website footer elements for supplementary information.
Ensure website responsiveness - a website has to be adjust across all screens
Ensure compatibility with all major browsers
Provide visitors with attractive and simple design - example: Google Material Design, Bootstrap etc ..
Assure consistent efficiency / loading speed of website content
Dynamic content - let website that adapts its content to the needs and interests of the user
UI adapted to content - documentation, products websites, forum, tutorials, articles - everything has to have a devoted interface. There is no single solution that works equally everywhere.
Order and check links - no broken links leading to nowhere
Assure short, legible and descriptive links
Ordered and clear structure of links taking into account categorization of content and its scaling in the future
Manage robots.txt to include necessary data and exclude unnecessary links
Submit website to the search console / webmasters / any of the major search engines
Map XML sitemap for search engines
Map HTML sitemap and site navigation for visitors
Ping search engines of updated website sitemaps.
Make sure to use a structured markup, H1 for a page title, H2 for a section sub-title - including keywords
Supplemented image Alt attributes and descriptions for every image
Supplemented meta data - attractive titles and descriptions including keywords
Complemented meta data, titles and descriptions for social media / sharing
Placing the most important content of a specific URL ( in terms of visibility to the visitor ) immediately after loading the page.
Avoiding duplicated content, or complementing it with additional content, as much as we can
Provide some methodology of image / media optimization
Depending on content placement, and from time to time, provide reasonably placed links to external high-quality websites
Include rel="nofollow", and / or "external", and / or "sponsored" in most of cases of outgoing / external links
Provide only top quality content which should be better than competitors content, at least :)
In cases of specialised website, academic or scientifical content, the reader will expect extended and comprehensive content.
Include relational content - Instead of single texts, creating a series that lead the reader, in a meaningful way, from one text chapter to another
Use media / images / videos reasonably and include interactive elements ( charts, maps )
Frequently update website's content and provide direct communication channels with users ( maybe web notifications, mailing lists, social media .. )
Minimize the use of pop-ups and alerts, and replace them with dynamically generated content