@evolutionary, it's all about immediacy and emotional regulation.
Immediacy means immediate praise, consequences, instructions and actions. No long lists of things. "DD can you brush your teeth, get your bag and get dressed" is about 50 actions, none of which will be remembered. We had a picture list of morning tasks on the fridge and would point, "DD what comes next?". And praise everything, but not gushing. So it's, "good job" for the teeth. But anything that requires effort or concentration, "I see that you really tried with that, are you proud of yourself?" "that tree in the picture is great, did you work on that a lot?" Internalising both the action and the praise. Never "OMG you're amazing" or "fantastic picture".
But bad behaviour, "DD if you do that we will have to leave (or some other immediate natural consequence)" she does it, "sorry, we have to leave". No long lectures or value judgements or disappointment. Just the consequences, very swift and with empathy. ADHD kids get a LOT of negative talk and almost no positive so trying to address that is important. Have a positive story about your child.
Emotional regulation, back to the fridge. Big graphic of faces with emotions. Teach them to recognise their mood and name their emotion. Empathy is really important. Both to have it for them and to teach to them. So any outburst or tantrum should be met with, "You're really angry, I'm sorry" and when they can talk about it, "what was going on DD?" Again short and empathetic. If they get angry/upset again talking about it, "we'll talk when you can".
Don't expect too much, make sure you run through all the things you could have done before their behaviour. Hungry, tired, too much stimulus, thirsty etc. And have age- and ability-appropriate expectations.
The best book is How to talk so kids will listen and listen so kids will talk. Really good.