Medication and maturity. Those are the things that make the most difference. The maturity one is frustrating as often ADHD means that in some ways they mature more slowly (DS has always been very insightful and mature in other ways but I don' tknow if that's the ADHD or his personality). The maturity allows them to recognise and articulate the challenges and take note of things that specifically help them. DS does a LOT of exercise and has learnt that without it, he finds everything else harder. Similarly, he has started to see his strengths and weaknesses and to accept that yes, he's good in a crisis but no, he's bad at office/classroom based repetitive tasks.
At a young age, I think getting them out and about as much as possible is essential. For DS, this really needed to be in a formally organised sort of way - he's not hyperactive so any suggestion that he come for a walk or whatever was not enthusiastically greeted. But he loved loved loved his sports group and went every week until he aged out and enjoyed swimming lessons etc. Then we had a little gap which was challenging - combination of Covid and age/lack of maturity (exacerbated by the ADHD I know realise) - and then he took up formal sport again from about year 5 or 6. during Covid him and DH used to do circuits in the garden/house which did help a lot. He needed a routine where he KNEW he was doing xx class on yy day at zz time.
Also, and this one is controversial, we had and still have a very different approach to screns to many of his friends. He doesn't have limits. He only has what I think of as guardrails - he's not allowed to be on screens/PS etc if he had a sport activity, family activity, homework etc. LONG before we knew he had ADHD we realised that trying ot do bedtime stories hyped him UP before bed while watching random things on youtube calmed him down. It was weird and counter-intuitive (and we were judged harshly by others).
Sleep is another one. DS was a nightamare sleeper. Just could not/would not go down from when he was a baby. Woke up in the night regularly until he was about 7. It took me YEARS to accept that his sleep needs and pattern need to be different and that getting sleep was the most important. So when he woke up in the night, he'd come up to our bed, DH would go to his, and we'd ALL get sleep. Even after he stopped waking up, he would often land up sleeping with me as he couldn't settle by himself so he'd come and sleep in our room and DH would sleep in his. Once he started sleeping in, I initiated a rule that I would protect one proper lie in a week, no matter what. Of COURSE I'd rather he was goign to bed at a reasonable time and getting up at a reasonable time, but that's not how he (or DH - also ADHD we suspect - for that matter) operate, so forcing it just lead to cumulative sleep deprivation and a corresponding increase in emotional disregulation and poor behaviour, whereas accepting that on Saturday/Sunday he would simply sleep until 11 meant he at least got that one day a week with a very long sleep cycle which he really really needed.