I explain to dd2 what the problem was and why it made the other person or me sad. Usually once I explain that she offers the apology herself and offers cuddles. If she's upset I take her away from the situation to calm down then do the explanation.

I try to model the behaviour I want, so always use please when asking them to do something and saying sorry or apologizing if I've done something wrong. I don't believe in trying to be right all the time because it's just not possible.

Of course some days none of this works and we all end up in a screaming heap :-/ manners will come eventually I've found. I try to be consistent and I even get compliments in public now for their manners.