Another thing that I try to do is enlighten my difficult child as to the intrinsic value of why he should do something. My son is very ODD, so everything I ask is routinely met with a "no". Explaining why something was important, and how if he did XY&Z would effect his life, was something I started with him when he was very young, and now, it is really how we operate. I am not sure this is the best method - however - it worked so well, at the time, that I still use it, with variances here and there.
So for instance, if I want him to take out the trash, I usually tell him he needs to take it out, because it is the day the city picks up trash. We just can't wait to do it, because then it won't get picked up! Or if I need him to clean his room, I explain to him that if he doesn't, mold will grow in that coke can that has been in his room for days. Gross!
One point I also try to make, if I can incorporate it, is how him doing what I ask might affect the dogs. I know that sounds wacky, but he is completely obsessed about the well beings of our 3 dogs, and he feels responsible for them, so I try to use that to my advantage. Like how if he doesn't take out the overflowing trash, the dogs could get in it and get sick. Or he needs to pick up the backyard so that the dogs don't ruin chew his things. That kinda thing - I tend to be very creative.......and probably bizarro with it.....but it works for him and that is what matters. I can concoct a story a mile long about why he needs to do XY&Z, in a half second.
I am sure, most would say that in the easy child world children just need to do as they are told - but when your child NEVER does what they are told without a series of "no's", and then a tantrum, you have to get creative.
I remember one time my son's second teacher called me, irate, because my difficult child was making fun of a girl with Spina Bifida. He was calling her horrible names, and the teacher called me to "talk to him" about it. (Greaaattt!) Anyway, instead of reprimanding him, or scolding him, I explained the situation to him. No one had even told him that the child had a disease, he just thought she was "weird". So when I explained the disease, all the symptoms, and the prognosis, he did a full 180. He never made fun of her again. I thought that was extremely powerful. I decided then, and there, that with my son information was power, and I needed to capitalize on it.
Just my 2 cents................keep the ideas coming, I think it is helpful for all.