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.
How I store things I want to read later February 12th, 2019
A System for Remembering What you Read October 6th, 2018
Takeaways from the Mind Illuminated September 19th, 2018
Setting Tinder to auto-swipe right on anyone that's a keyword match September 6th, 2018
✍️ I made a RescueTime plugin for Mac Menu Bar August 2nd, 2018
This is Water by David Foster Wallace (Full Transcript and Audio) July 29th, 2018
Flashcarding is a superpower; don't drown in them July 27th, 2018
Why do we work so hard? July 22nd, 2018
Augmenting Long-term Memory July 7th, 2018