I’ve contributed to the phoenix lib. it was only a read me update but it still gives me the warm fuzzies.
Honestly the best way to get start is to work in the docs. There is always room for more docs.

Most of my (self-perceived) contribution to elixir ecosystem is coming from real world experience, like sometime i use a library/a module but i can’t easily figure out what’s it’s supposed to do from reading documentation. After i figure it out with correct understanding i would make a PR to the repo to try make adjustment to docs to make it easier to understand.

FTR, I’m not an Elixir contributor myself.

Some useful links:

https://elixir-lang.readthedocs.io/en/new-guides/repo/contributing/

Learning about metaprogramming is great in order to extend any language on your own, you’ll learn about the internals along the way.

But you could just build a small library, without much thinking. As long as you start.

Very friendly community.