Same here, I used to waste so much time mindlessly scrolling social media feeds throughout the day. Setting designated times to check social has def boosted my productivity big time. Another habit I kicked was constantly checking email - now I only check at set intervals which keeps me way more focused.
This was a while ago, but the first thing that came to mind. In high school i spent untold hours playing video games. Somehow my not-yet-fully-developed brain recognized this was unsustainable, so consciously did not bring any of my systems, etc. with me to college.
Eventually the pull of the habit just sort of died off. Still enjoy some nostalgic n64 games with my brother-in-law a couple of times per year, but otherwise all that daily energy is redirected to other hopefully more fulfilling (for me) pursuits.
BodySherpa