Without taking medication, I think the most helpful thing you can do is make sure your environment is working with your ADHD instead of forcing yourself to work in a not so ADHD friendly environment. There's a YouTube channel called How To ADHD that has good tips for stuff like that

I divide bigger tasks (like writing an essay) into smaller tasks and write a checklist and give myself rewards when I complete them! Ans having an adhd space is also helpful

Timers with labels for what task I’m completing, clear storage bins, organizers, having a place for everything, a day planner/bullet journal, using multiple calendars and trying to keep them all updated, (one virtual, one on paper), regularly going to therapy to learn coping mechanisms for when I’m frustrated with myself( and a ton of other stuff tbh), rewarding myself for completed tasks.