For me, simply doing less stuff, but being more "intentional" or "mindful" or whatever you want to call it, is the key. For example, I used to have magazine subscriptions, RSS feeds, piles of books, hobbies and side projects, and tons of stuff I wanted to do or places I wanted to travel. Those things, which were entirely elective, added to the overall burden of feeling like I couldn't keep up.
As I've aged I've also switched from "this is what I want to accomplish" to "this is how I want to spend my time". I do a lot more reading, staring into the distance, joking around, etc.