My first real experience programming was when I was 19, before ever having a class, teaching myself PHP/JS on the job to write custom wordpress themes. I started writing inefficient spaghetti code and progressed into writing object-oriented, then started looking at performance. The performance aspect was definitely the deepest rabbit hole.

I would say that I learned more doing that than I have getting a CS degree at my state school (aside from writing performant code, which classes have helped with). But it is mostly because I viewed getting good as a way to escape from some bad circumstances at the time - every word I didn't know was a low-hanging fruit waiting to be picked. I did a lot of reading, and I practiced at home in my spare time as well.

I got really good at front-end stuff and learned how to use the terminal so that I could host and manage our company's websites on a digital ocean droplet (running centos). I learned a lot on the linux terminal - writing bash / shell scripts, managing configurations, etc. Improved speed a lot by configuring apache... then again by redoing things in Nginx on the next site, which I've preferred since.

Since I've gone back to school, going overboard on programming labs has also helped a lot.