Agree that a lot is personality, but I think that there are harmful spirals you can get into inadvertantly and there are things that I did which I'd recommend
(And some which I don't!!)
Most important thing I think was always trying to see the person and the intention behind the action first rather than seeing the behaviour first as a problem to be solved. Relationship and curiosity have always probably been my 2 biggest priorities and that seems to have helped.
Best 2 books have been How To Talk... and When Your Kids Push Your Buttons: And What You Can Do About It.
DS1 was not actually diagnosed with ADHD until he was 10. The bigger factor I think was I was diagnosed with it when he was 8. It helped me put so much into context which is why I suddenly saw it in him. I didn't have a lot of support during the toughest years which were probably ages 3-6. I should have sought support at this time, but a combination of not thinking there was an issue/assuming I'd just be told to be stricter/nobody else was raising concerns. I wish I'd seen this: https://www.instagram.com/p/CzBhyIvOpni/?utm_source=ig_web_copy_link&igshid=N2ViNmM2MDRjNw==
I am quite laid back. I tend to see everything as a collaboration and I don't see my role as being to mould him or fix him. I see it more as it's his life and I'll help him do the things that he wants to do.
We did a LOT of work on emotion coaching from when he was about 4-6. I can't remember everything that we did but lots of talking about ideas to calm down. The sensory jars etc have never worked for him. (I have since learned that this might be because I only ever brought out stuff like that when he was already enraged, rather than just having it as a normal thing that we did when he's calm too.)
Taking myself to another place to calm myself down rather than me exploding as well which wasn't v helpful.
Things improved when we cut screen time. I'm embarrassed to say but when he was younger he was probably having 12 hours of screen time a day. He was basically on a screen all times that he wasn't at school. It was actually when we did the ADHD assessment that I calculated it and thought - oh shit, this is terrible. I'd previously tried to cut it down to half and this resulted in him spending the entire of the other half of the day asking me when screen time would be, pinging around the living room, asking me to do things with him, complaining of being bored literally one second after we finished an activity and generally driving me bonkers. But once we cut it down to max 3h this stopped him from focusing on it for the rest of the day and he would do other things.
Another helpful tool was what I later learned is called a token economy. I made 6 behaviour related goals, worded positively (e.g. instead of "not shouting" "speaking respectfully") and 6 target activities (e.g. cleaning up, being helpful) and put them on the wall and throughout the day if he was veering into a behaviour that we wanted to stop I'd remind him "Hey, that isn't a very respectful way to speak" using the same language as on the chart - but crucially - I would not reprimand or get into an argument about it in that moment, it would just be a very short reminder/warning and sometimes he'd then stop. If he did not stop I just ignored/walked away. This helped SO much because previous to this I'd been getting into multiple battles with him all day every day and they would always always always escalate and I had no idea how to stop that.
At the end of the day we'd have a debrief and I'd tell him all the tokens that he had earned. I didn't explain all the ones he hadn't earned unless he asked. He very rarely asked, because he already knew, he didn't need me to go in and hammer the point. The focus was not on what he'd done wrong but what he'd got right. The tokens could be used the next day (for screen time!) but there was also a bit of - you save up and can get extra. We would also sometimes have a bit of a pep talk/brainstorming session about how he could earn a particular one the next day.
Learning about Executive Functions has helped. There are some good resources out there - Seth Perler, Russell Barkley, ADHD Dude, ADHD Essentials Podcast.
More recently I've learned more about emotional regulation and the nervous system. This isn't a tried and tested recommendation because I didn't have this info when he was younger, but I am using it with my younger DS (5) who is probably not neurotypical. Mona Delahooke and Stuart Shanker are probably the two biggest players here.
Lastly I mostly followed what I thought of as "gentle parenting" but I think the gentle parenting landscape today is more extreme and not as helpful. The concepts of emotion coaching, seeing the emotion/need/communication/stress level behind the behaviour, controlling the environment, collaborating, problem solving, being on your child's side, being positive, understanding sensory needs are all fantastic. Some of the more rigid ideas like never using reward and punishment or all behaviourism is bad, automatically adopting a low-demand approach for all children are IMO not so useful. Modern behaviourism is very positive and can be really excellent and have some good tools, even though there are still aspects that I dislike. There is a course on coursera called ABCs of Everyday Parenting which is very good particularly for explaining effective praise, token economies, finding a positive opposite behaviour, "shaping" which is breaking a behaviour down into steps to work on. (If there are more tips I haven't got that far yet).