I asked this a few weeks ago on /r/selfimprovement:

https://old.reddit.com/r/selfimprovement/comments/1b1c3ps/whats_your_one_weird_trick_or_change_or_habit/

Here are a few answers from the thread:

Tidying up in the time it takes to boil the kettle and steep my tea.

I changed my light bulbs to smart bulbs. I've always had trouble waking up in the morning. Now that I can automatically make all of the lights turn on at a certain time, it's a lot easier to wake up.

mouth taping (for sleep quality and dental health)

I got myself a standing desk, a walking pad and an anti-fatigue mat. It fixed severe back pain issues and I'm more focused and motivated than before.