Time well spent
Seems like figuring out how to be really good at learning and how to procrastinate less would have big returns on time invested, so I like to think and read about them. Spoiler alert: I haven't figured any of this out yet.

As for learning: flashcards have been really helpful since I started using Anki in 2013. They help me feel like I can learn anything without having to worry whether I'm wasting my time because I might not remember it in a year (because now I can be sure I'll remember it in a year if I want to). Here are some details about my system. I also try to spend 30-60 minutes studying every morning before work, but it's a tough habit to keep up, as you might imagine.

As for productivity: start with my struggle with productivity and the results of a productivity experiment. I've also been borrowing techniques from meditators designed to help cultivate effortless, sustained attention.
Updated: September 19th, 2018

Sources, notes:

Key: ✍️ is a blog post, 📘 is a flashcard, no emoji means notes & highlights.
Augmenting Long-term Memory July 7th, 2018
Productivity frustration: update March 5th, 2018
Productivity frustration February 22nd, 2018