The Elementary Series covers important topics that can be applied broadly at all levels. This is not meant to be a lesson from me to you, and you can read more about the motivation behind this in this feedback post.
Newer players should find this particular useful, and the information should be relevant in any patch. They are also not limited to Terran.
This page serves as the content page of the series, and each topic will be posted separately with an [ES] tag at the title. This is still a work in progress, so the topics below may not have a link and they are not exhaustive. I welcome topic suggestion.