Make sure that the parents don't spoil them as a child, so that when they becoming a teenager, they won't expect to be living a life with luxury and not having to work for it. Being positive and hopeful about a teens behaviour is better than putting them down and give them strict behavioral expectations. In addition to that, it is better to keep them motivated to do good, not tell them that their behaviour is bad and they will never change, encouraging them to be a good person and have good behaviour is what they should do.
P.S I'm 14 so I don't rlly know if i was that helpful-
