Meditating is a big one for me - it just improves the quality of everything. I beemind meditating every day (I’m trying for 3 hours a day) and beeminder has massively increased the amount I meditate and boosted my consistency.
Another one is a memory game called dual n-back where you are presented with a sequence of sounds (letters read aloud) coupled with 8 positions on a 3x3 grid, and you have to press buttons if the thing displayed matches the thing N items back in the sequence in sound, position, or both. N increases as you get better at it. It’s amazingly good at noticeably increasing the amount of stuff you can hold in your head at a time - like a RAM upgrade for your brain. You can actually feel your brain expanding. Thanks to beeminder, I’ve been dual n-backing every day.
Another daily one is taking a 10-minute walk outside every day - a small thing that makes a huge difference in life quality.
Then there’s regular processing at the daily and weekly levels (GTD style), where you go through all the stuff you’ve accumulated (mail, email, notes to yourself, stuff in your head), get it all out of your head and in one place, and go through it to make sure you’re keeping track of all your projects and next actions. I’m still working on getting this down.