Well, this is a tough one but the answer really doesn't vary much by the age. However the consequences vary greatly by the age. The place to start is with "building meaning" Have you ever taken a puppy for a walk using one of those retractable leashes? The more line is given out the more the dog thinks he/she is in control and the wider he/she roams. When parenting there are two basic approaches. Give more leash and then reel in as necessary or keep a tighter leash and lighten up when possible. What parents need to do is know their child and what will work best. Of course always having to hold the leash and keeping it short takes a lot of time and effort but it really is the only way that children learn about consequences.
Now if the child is older and you try to impose greater restrictions then they will fight it more so it is best to start when they are younger and you can see which methods are likely to be needed whith which child. keep in mind that what is equal isn't fair and what is fair might not be equal. Sit children down and let them see the big picture. Help them to chart the course but then you be the one on the wheel and let them take turns learning the controls. As children get into their teens they begin to recognize some of their own problem areas so it is good to have them identify for you what they want to work on and how you can help them.
Keep in mind that the child with the biggest problems is still just a kid first and someone struggling with coping second and not the other way around.