Welp. Discipline has many forms. It depends on the individual and what they plan on getting done to achieve a goal (ie routines, studies, progress for a milestone, etc.)
If you're someone with ADHD, societal expectations of what is good practice for being "disciplined" is not going to work for you. People with ADHD sometimes need specific tools in order to achieve short term and long term goals.
I work full time on my comic. Every day, I work on the page work for 5-6 hours. This could be rough drafts, tight roughs, line art, flats, or coloring. I try to focus on one of those phases. (My main script is finished, so I don't work on that much anymore.)
Some days, I have a hard time focusing, so I jump between phases depending on what has been done so far for page work. And sometimes I work on extra stuff for my Patreon instead. A break can do wonders to help you refocus onto your main projects.
I usually run off of self-determination, but that doesn't work for everybody (and it sometimes doesn't work for me lol.)
So here's my general advice for getting things done:
- Visualize or write down your overall goal for the thing
- Plan out smaller milestones that will help you achieve that goal
- Determine how long it may take, then add "cushion time" on top of that
- Don't try to go 100% for consecutives weeks; plan time away from the project
- Reward yourself for the small milestones or just a good day's work! I use little wooden Moomin stamps in my day planner at the end of each work day. That allows me to see what I got done for the day, and adds a little joy to it. :}
I hope any of our advice here in the comments helps you out!