Reddit mentions of Systems Analysis and Design: An Object-Oriented Approach with UML

Disclaimer: I'm an undergraduate and don't know shit.

I think the best way to learn is from the small parts, up. So, first learn a structured (preferably OO) programming language. Python will do, but I'd recommend something with compilation and static typing. Python is great for scripting and has its purpose, but designing and implementing a complex system in Python is a nightmare. After learning that, learn how to write your classes, methods and just generally structure your code better. I highly recommend Clean Code for that. After understanding good class design and code structure, start learning about higher-level concepts on how those well-defined classes should communicate with each other and be decoupled. Important concepts to learn are coupling and cohesion, polymorphism, inheritance, etc. All the basic OOP concepts. From there, you can move onto architecture. The book I used in my courses was System Analysis and Design, but there could very well be better ones out there.

Edit: Oh, and it's helpful to at least be knowledgeable of common design patterns. I really like SourceMaking's approach and explanations, but once again there's tons of good resources out there.