United front. It is critical to present as a united front. Have discussions in terms of parenting outside the ears of the children. It is ok to let the kids know you're talking and making decisions together as a "team" and teach the kids to wait for a team response when possible. Try to target a 1-2 behaviors at a time for improvement and decide how you will address and then be a consistent team!
Be a team. All members of the "team" need to agree on the main aspects of their plan ahead of time and stick to it, backing each other up at all times. They (i assume you mean mom and dad) must also try not to undermine each other's judgment in front of the child.