How did you teach yourself structuring large projects and test driven development? Did you have any senior engineers mentor you when you just started, or did yo

How did you teach yourself structuring large projects and test driven development? Did you have any senior engineers mentor you when you just started, or did you just force yourself to pick important skills in software development. I ask because I work remotely a lot of the time, and I am skilled in creating a solution, but I am always worried about if it will be maintainable over time and not be overwhelming when I add features.