Develop habits. They tend to work much better than relying on willpower. Especially when you’re feeling down or less energetic or inspired.

As mentioned elsewhere, start with the tiniest, lowest-willpower possible variant of your habit. Once you’ve been doing it for 3-4 weeks, you can increase the scope or ambition of the habit. Do that for another 3-4 weeks, iterate ad infinitum.

For managing scope creep, develop systems or processes for deciding what to work on. Make a habit of working only on things bubbled up by the system.

That last bit is interesting.

How do you design a system for bubbling up relevant habits to ingrain (or increasing scope to established habits)?

Oh, wow, you took that in a direction I didn’t expect. I meant that you might benefit from a system to manage scope on the projects you mentioned struggling with scope creep on.

But applying that to the development of habits themselves too is a really interesting idea. I’d never thought of that before and am not sure how you’d approach it.

1) Acknowledge that your brain is made of meat and give the meat what it needs: good food, exercise, 9 hours of sleep a night.

2) Ensure you understand the "why" of what you're trying to do.

3) Ensure you have a clear "definition of done" or "definition of good enough" for your tasks.

4) Try to identify fears related to the tasks, to take those fears seriously, and to get them solved.

Asking myself every time that I am tempted to break my discipline: "do I want to be the kind of person that just doesn't get <insert anything: tidy up before bed, be always punctual, finish this review on time, commit&push before leaving, etc> done? Surely not. I can do better. I can be be a role model" ... Sounds silly, but works wonders for me. It works so well I keep it as a secret so that others won't know to achieve my level of discipline. I also think of how disciplined my mother is and keep that in my mind as a guiding force.

Develop discipline by starting small. For example, push away from the dinner table while you still feel hungry. At work, do the most difficult and important tasks first. Discipline derives from attention. Ask yourself, "Where is my attention?"

Find something non-work-related you hate or dislike doing, but is good for you. Do that thing at least an hour 2-3 times a week for the next year. "Hobbies you hate" is a good way to get started

Working closely with people (friends preferably) who have higher "discipline" than you, and seeing how they grind their way through a problem is instructive sometimes.

The fear of poverty keeps me "disciplined".