ianis's Book Journal
Fluent Forever: How to Learn Any Language Fast and Never Forget It
This book is a treasure for anyone who wants to learn a new language.
My main takeaway though is the SRS — use of the cards, the so-called "Leitner system". Basically you put new words on your flashcards and review different "level" stacks every day (there's a special schedule). Doing this now and am finding this very efficient.