My advice for parents is to be consistent with your difficult kids. A strong willed child will need good, firm boundaries and the same rules every day, no matter what. It is exhausting and easy to just say "Do what you want". But now having a nine year old who has great character and makes (mostly) good decisions about how to behave, this advice stands the test of time. I would go to a friend's house and her children would be jumping on the bed with shoes on, or running through the house with food or something, and I would have to say to my son " We don't do that at home, we don't do it here". It was hard to have to do that, but he was not the type of child that could change his behaviour when he got home. My friends soon had to learn not to be offended, but I had to stay strong with our rules, or I wouldn't cope when I got him home. It's a lot harder to undo bad behaviours than to instill good ones from the start. Of course, this means getting your husband, grandparents etc to have the same rules for your child, too, to avoid confusing them.
Domestic Goddess Mum of Four!