Project(s) or exercises to learn sysadmin skills?

I've been trying to study to became a skilful Linux user but it's difficult to come up with ideas regarding what to do in order to learn system administrator skills and systemd (or those BSD style scripts). I have made some Bash scripting and blocked some addresses with firewall and other small things like this but I haven't got really deep yet.

I have a virtual server space bought from an ISP which might offer good possibilities to do sysadmin things (I have used it to run Screen with IRC).

Which kind of projects or exercises it might be useful to take up in order to get really into this system administration world and to use the features of Linux extensively? Ideas are welcome.