Great question; my first-ever ticket was to set my development environment up, which was quite involved. My first contribution at work was to update the env-setup documentation :)
After that, I took tickets that involved small code updates, like HTML changes, or including a table column that allows an object to receive a new attribute. Most of what we code on my team ends up in front-end production, so I see the "fruit" of my work in a very visual way. Seeing my little changes reflected on our production sites gave my confidence such a boost.
I would say that, so far, my biggest trip-ups at work have been GitHub-flow related. Which is why I shout from the rooftops: "Get involved in opensource!!!" In my opinion, it's the closest you can approximate a professional coding environment, and it's great practice in code review, reading, understanding and modifying code, avoiding adding code debt, etc. If you're into Rails and/or JS, the Dev.To opensource project is just stellar!
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