From a young age I always expected them to be kind and polite. Before we went into shops when they were little I would remind them to say please and thank you, to wait nicely to be be served etc.
I always listened to them carefully. We never did any of that naughty step, removal of toys nonsense - never turned family life into a battle of wills. they had a cosy corner instead - not a punishment, but a place to go and calm down with a blanket, cuddly toy, book etc so that they learned to manage their emotions themselves, not feel emotion is something that is repressed and dictated by others. As a result, I had an ASD son who has never had a meltdown and another son who is one of the most chilled people I've ever met. I came from a very aggressive, shouty, theatrically emotional family and had to learn to curb that behaviour myself as it makes DH feel ill (and me too, I've realised.) So... we just nevewr shouted, never bullied, never battled.
People think that means we were soft but we weren't. If DS1 threw a toy in anger and it knocked over a vase of flowers, for example, I'd say 'Oh dear,' calmly, then get him to get a cloth, mop up the water, put the flowers in the compost at the bottom of the garden, get money from his piggy bank, go to the shops, buy more flowers and a new vase from the charity shop etc - all calmly, all with no anger, just 'Oh, shoot, this is what we all have to do now, bit inconvenient, eh?' And he soon learned he couldn't be bothered to wreck things.
So we modelled kindness, consideration, responsibility for actions, consequences of actions, all with no anger, no shouting, no drama. Learning to self-soothe when you are angry or upset is the single most useful skill I taught them. I know so many people who thought I was soft, because they preferred to be heavy-handed with their children. They are the ones who had really tempestuous teenagers who smashed doors and got into fights.