You should start by following generic SEO advice, since Moodle is just like any other website.
Where you are possibly going to get stuck is that most of the content that you would want Google to index is only visible to students.
You may have to add static pages in order to optimise your publicly visible content.
See https://elearning.3rdwavemedia.com/blog/how-to-add-pages-to-moodle-using-the-static-pages-plugin/3277/
Regards
Brendon
Where you are possibly going to get stuck is that most of the content that you would want Google to index is only visible to students.
You may have to add static pages in order to optimise your publicly visible content.
See https://elearning.3rdwavemedia.com/blog/how-to-add-pages-to-moodle-using-the-static-pages-plugin/3277/
Regards
Brendon