I disagree with lots of advice here. My strategy to solidify my linux skills was simple: commit to linux desktop. We spend most of our time on our desktop, may as well let that time earn you skill points. I picked ubuntu and use the same on servers. You naturally learn a bit every day through daily use. This really adds up over time without extra effort of using a side system. Getting good at windows or osx is a wast…
It is trendy to hate C now, but if you want to understand a Unix-like OS I think it is mandatory and they go hand in hand. Otherwise, you will have no idea what kind of interface your higher level language is abstracting. It's ok to not like it, but don't let that dislike be due to lack of understanding.
I spent a lot of time in assembler too, and yes it has benefits for learning. Im also not recommending a high level toy like Logo.