May get flamed for this from those who have 'difficult' children but I'm a firm believer that children's behaviour is generally caused by the parents' parenting style.
We are quite strict with our DS and, although I'm biased, he is pretty well behaved. He says please and thank-you (always!), eats nicely most of the time and is a pleasure to be around 99.9% of the time. Obviously, he has his moments as do all children but he is generally very good.