I'm currently on a "rationality as 'skills you practice'" kick. I'm really into subtle cognitive skills. I do think they eventually pay off.

But, realistically, if you have a major problem in your life, my experience is that the biggest effect sizes come from radically changing your environment.

Move in with new roommates.

Get a house in a new neighborhood.

Get a new romantic partner.

Get a new job.

Move onto a new team at your current job.

I'd count "install a serious internet-blocker on your computer that kicks in automatically at regular intervals" as an "environment change", since we do live our lives largely "on the internet."

You want your general life situation to feel like flowing downhill, not having to trudge uphill. Often, lots of little things about your physical and social environment make things frictiony, or demotivating, 

When I briefly lived on a boat where going to the bathroom required completing a minor obstacle course, I was surprised how much I just automatically got enough exercise and lost weight. I haven't succeeded at finding a way to live longterm with those properties, but, the proof of concept had a pretty enormous effect size.

If you feel like your life is sorta stuck, you aren't very happy, or productive and it all feels sorta shitty and intractable, consider rerolling some major aspect of your environment. This is pretty effortful, and if your life sorta sucks it may be challenging. But, I think it's more likely to work that a long slog of "try to get an exercise habit, try to get incrementally better at focused work."

You can change environment in an intentional way ("On reflection, my job does just suck. Or, something specific sucks about my team, let's go talk to my manager and try to switch teams."). But, anything that radically rerolls your environment has at least a decent chance of rejiggering whatever was making things suck, even if you don't have a good model of what was wrong.

But That's Expensive

Since I first published this, @samuelshadrach in the comments noted:

Random hit and trial has large time and money costs. More guidance on what to reroll when seems important to me.

Yeah. There's a better, longer version of this post that goes into a lot more detail here. Changing major life circumstances is obviously not something you can do every week or month and even doing it once a year is kinda A Lot. 

The most important thing is to have this in your option-space. If you're trying a lot of micro-optimizations, but you have a nagging feeling that your life situation is fundamentally off, at least consider fixing your overall situation with more drastic macro-moves.

If you're not sure whether to press the "re-roll environment" button, one thing to look for, is: 

When you talk to your friends about your problems, instead of being like "oh yeah I have those problems too", are they more like "uh, are you sure you're okay? This doesn't seem normal." 

A major wake-up call for me was when I was working at a job that was stressful and I came home crying a couple times a week, my then girlfriend said "hey, um, this isn't okay. This is not how jobs are supposed to be." And I'd say "but I think there's a rare opportunity at this job to do something really meaningful" and she said "idk man it's not that rare, there are other places you could work that do similar kinds of things."

This unfortunately only works if the situation is pretty extreme. If things are more subtle, I don't think there's a shortcut to knowing what to do. My advice is: Think carefully about the nuances of your situation. What feels shitty now, or what are you spending a lot of time on? What would make you happy, and when you've been happier in the past? Talk it over with friends or therapists, think it through.