The one thing nobody has mentioned here is the most important and often least applied. I'm talking about discipline. That doesn't mean shouting at kids and hitting them - though a light cuff across the back of the head ( a 'Gibbs') is often a handy warning or reminder - but a clearly laid out code of conduct and set of expectations, violations of which lead to meaningful punishment. Grounded kids stay at home evening and weekends. No TV/gaming/computer/tablet for a week should mean just that and be adhered to. Even an undeveloped brain can make the connection between forbidden action and unpleasant consequence. More importantly rewards should NOT be given for good (ie expected) behaviour, but only for going 'above and beyond' expectations.

In parallel with this should be a gradual increase in freedoms and privileges. It starts with "What kind of cookies would you like?" for pre-schoolers and by 16 they get to choose their own clothes (within budget). At the same time as increasing privileges, there must be increased responsibilities - by which I mean what Americans call 'chores'. Tasks and jobs that must be done if privileges are to be retained.

The worst thing you can do to or for a youngster is to do everyting for them until they are 16, 18 or whatever, then suddenly remove all support. This is what happens too often (especially with boys), with the results we see.