Resolve to make your dealings with your child's other parent as pleasant as you can -- even if he or she doesn't.
If your ex knows how to get under your skin -- and uses this knowledge unfairly -- resolve to keep your cool anyway. One tip is to have a friend with you when you have to see your ex in person; the mere presence of another person often calms the mood.
Don't hang on to old resentments, especially when your children are present. Take time to calm down and remind yourself that the remaining connection to your ex is solely about the welfare of your children.
Bite your tongue when you are tempted to speak ill of your ex in front of the kids. The best outcome of badmouthing your ex is that your children will feel uncomfortable. At worst, it will backfire on you: Children who are old enough to understand will likely feel a responsibility to defend your ex, further complicating the situation.
The same rules of good parenting you believed in while you and your ex were living together are still important. Talk to your ex about how to handle discipline, school projects, health-care matters, extracurricular activities and other situations you both need to have input on. Compromise whenever you can.