No matter what you choose to learn, it's good to learn how to learn.

You have the free "Learning how to learn" course on coursera : https://www.coursera.org/learn/learning-how-to-learn

And I'm currently reading a book called "Ultralearning" by a guy called Scott H Young who I imagine is the type of person to be on hacker news and be like "Hey, thanks for recommending my book!"

https://www.scotthyoung.com/blog/ultralearning/

The book so far is great, there are certainly some principles which may seem obvious but in reality they need to be acknowledged and used effectively. Overall it's a clear read and gives a pretty clear way to get started on learning a ton of things in a short amount of time.

No shortcuts though, still a ton of effort involved.