Don't forget to learn how to write a GenServer from scratch. I lot of people I've met who hop straight into Phoenix forget to learn the basics of GenServers (and processes in general).
This is great, I have been teaching myself everything and there are a lot of day 1 things I learned way too late, this is extremely valuable, thank you!
Here's a stupid example I whipped up:
https://gist.github.com/amorphid/3dec7028b05bd10f6ff3180d199...
^^^ you wouldn't ever code it that way, but you should (in my opinion) know what each line of code is trying to do.