Mattias Geniar posted an overview of how to take care of SEO from a technical standpoint:
If you're the owner or maintainer of a website, you know SEO matters. A lot. This guide is meant to be an accurate list of all technical aspects of search engine optimisation.https://ma.ttias.be/technical-guide-seo/
There's a lot more to being "SEO friendly" than just the technical part. Content is, as always, still king. It doesn't matter how technically OK your site is, if the content isn't up to snuff, it won't do you much good.
But the technical parts do matter, after all.