Basically reading how all these scalable systems are built, helped me a lot. Yes they only give you pointers. Then you can research more on those pointers and learn how to actually use these things in your own apps.
Yes, thank you for your response. Yes, I know about highscalability.com and such websites but the overview they give is very high level. I am looking to build something similar to the 6.171 MIT course - really hands on and concrete.