Exercising. In my 20s I barely exercised, certainly not reliably for any extended period. The longest stretch was while I had a roommate who was a former Marine, about 6 months. The man was a beast and I felt like a slug when I realized I'd played a video game for a few hours while he'd been out weightlifting and then running 5-10 miles. And that was his second workout of the day.<p>At 31 I'd gotten to 220lbs which, on my frame and at my activity level, meant obese. So I started walking a 5k trail near the office 3x a week. After a couple months I started jogging it (C25k style but not the actual C25k plan). By that point being out there was just routine, so why not run it? That was 8 years ago, and other than some stretches of time where I was recovering from an injury (so far only one caused by exercising, an impinged shoulder, the rest were caused by other things like car accidents) I've been a reliable exerciser and runner since.<p>A habit I broke was video games. I'd play games until 2-4am and then be exhausted the next day. In retrospect, they were a way of keeping my mind occupied while I was suffering from severe depression so I wasn't really alone with my thoughts. Then they became a routine or habit even after I'd recovered from depression, but were still negatively impacting my life because I was still putting in the crazy long hours. Mostly I substituted other activities like running or exercising generally, reading, spending time with friends socially, or more productive uses of the computer like programming. Exercising actually helped a lot because I was simply too tired most days to even consider staying up late playing a video game, even if I was enjoying it I had to turn it off and sleep because I was dozing off.<p>In this case, it was mostly the realization and acknowledgement that the video games were consuming too much of my time (and health) that led to a rather rapid change in habit. The various time fillers changed over the years, but I dropped video games practically overnight.<p>--------<p>EDIT to add<p>Journaling. I've tried a few times, and largely failed. I've found it helpful especially for dealing with stressful periods or depressive episodes. Just expressing my thoughts on paper gets them out of my head and the "dwelling" stops or is reduced which reduces my overall anxiety level or elevates my depressed mood a bit. But, like many people's efforts at dieting, I only did this for a period when I needed it and then stopped. When my mood worsened it "snuck up on me" and I'd have to rebuild these helpful routines.<p>I, recently, started journaling with a 5-year journal that only offers 5 or 6 lines per day. It's more of a log, but this also makes it easier to keep up with. I don't want a blank entry (at worst I fill it in a day late). This makes keeping a long form journal somewhat easier to maintain since it doesn't need to be daily or some other regular period, it can be weekly or even monthly, or following a major event (something deeply impactful to my life or my friends or family for instance).