Its very easy to get good with unix. I usually use the tee rule for this (look up tee on google ;) )
1) Get a good linux, you can start with ubuntu. After getting comfy with ubuntu try another os, debian,And eventually to the hardcore ones like Arch, Artix and others. Try to do your usual thing with commandline. For example, How to copy using terminal,How to open a file with terminal, How to get lots of terminals inside terminal. Stuffs like this (trick is simply go ahead and add "How to do it in terminal" ;) ) Google them up. (www.giyf.com) Try to rice your system. It teaches crucial aspects about the appearance,usability etc.
2) Get a good book. No starch press has some good ones, even O reilly gets you into shape. The trick to good book is simple: Get a book, read it. If you love it finish it. There are open source notes as well. Awesome cli github is similar.
3) Try to create your own tools using 1,2 this will allow you to bend your brain. Stuffs like How can I get hackernews comments in my terminal, How can I create a shell script to remind me that 20mins have passed (pomodoro) and stuffs like that.
I have some starred repositories and Some simple tools of my own (Aeres-u99 @github) to check for some example.
I think with this (depending how extensively you do them) you can be decent