My daughter is the worst of my children for saying no, but TBH we don't have an issue with things like them refusing to go into the car, etc. If it is something like dinner that one of them are refusing, then I give them a choice in the situation. For example I might say "you can eat dinner with us then watch TV, or you can go into your room and miss dinner but there will be no TV tonight". That way they are choosing for themselves, and they usually pick the thing that they were previously saying no to. A refusal to go to bed might result in "you can go to bed now and have a story, or you can refuse and I will put you in your bed without a story". So no real choice other than the choice to cooperate or not but 9 times out of 10 it works.

In other aspects of their lives I give them a lot more choice and I find that this has stopped a lot of the "no" reactions, especially from my daughter. So to daycare she often wears a fairy dress and gum boots. Or she might decorate her skin with her new pens instead of drawing on paper. I don't worry about things like that and give her a lot of freedom in that respect, so that when I say she has to do something she is more likely to comply because she knows I am not just making rules for the sake of it, if that makes any sense.