This checklist will help you set up your Drupal installation with some important contributed modules for Search engine optimizations SEO purposes. You can refer to my website checklist for developers.
Run the Lighthouse test against your website and review the test results and follow the guide to fix the issues. You can reach the 100 score by following all recommendations.
Enriches your content with metadata to let other applications (e.g. search engines, aggregators) better understand its relationships and attributes. You can enable the RDF module which is coming with Drupal 8 core.
Metatag module allows you to automatically provide structured metadata, aka "meta tags", about a website. In the context of search engine optimization, when people refer to meta tags they are usually referring to the meta description tag and the meta keywords tag that may help improve the rankings and display of a site in search engine results.
Install the HTML Formatter it's a simple module that lets you input a HTML tag to strings, timestamps, datetime, entities, etc... It will help you to change the displayed fields to have a specific HTML tags. Like changing some fields to have H2 HTML tag for SEO purposes.
The Linkit contrib module will help you to refer to your contents and having an internal backlinks. It provides an easy interface for internal and external linking with WYSIWYG editors by using an autocomplete field to select the content that you need to have it as a link inside the WYSIWYG editor.
The Simple XML sitemap contrib module is the best to me. Every webpage needs an automatic XML sitemap generator for SEO reasons. Sitemaps generated by this module adhere to the new Google standard regarding multilingual content by creating hreflang sitemaps and image sitemaps - Googlebots will thank you later.
The redirect contrib module will help you to maintain a canonical URL for all content, redirecting all other requests to that path. It will help you to avoid having the same page working on different URLs by redirecting all page aliases to the last path alias you generated. This module is a must to have.
Just like the redirect module but the Content Translation Redirect contrib module is for you if you are having a multilingual website. This module will be useful if you need to redirect users from pages of non-existent translations of the content entity to a page with the original language.
It's very important to provide an easy way for visitors to share your website content. While there are a lot of social share modules out there but I prefer Shariff or Share Everywhere. In order to make Shariff module work you need to read the important notes on README file. Sadly you need to download the JS library manually and putting it inside /libraries folder, you can refer to status report page after enabling the module to get the instructions too.