A week ago, I started with something called the Linux Upskill Challenge. It’s a monthly set of lessons posted by /u/snori74 (as far as I am aware, not the Icelandic poet come back to life with a passion for Linux). The set of lessons are to teach you about being the administration of a Linux server, with practical challenges. You start off by getting a server online (as suggested by /u/snori74, I chose a $5 server package), and weekday-by-weekday, there are short lessons on how commandline administration of the server.
I figure that, by now, I can call myself an average Linux user: I know enough to solve quite a few problems by myself and I know enough to search for the right solutions to my issues; however, I’m also clearly not to the level of the Linux users who will program their own widget to create an alternative to this or that program that they have an issue with. This program has really worked for me so far. I know enough to easily progress through the first couple of lessons, and yet each had really new information for me in the extensions.
I can really recommend it to anyone that wants to learn a little more about Linux.