http://coparenting101.org/ten-commandments-of-co-parenting/

1. Resolve conflicts without putting kids in the middle. This requires being objective about your children’s needs (and not confusing them with your own) and compromising when the situation warrants. Stick with a conflict until it’s resolved; don’t let a problem fester and then punish the other parent passive-aggressively or be difficult in unrelated situations.

2. Treat the other parent with respect. This goes a long way toward easing your relations with your former partner. It also provides a good model for your children; more than we are willing to admit, our children imitate our behavior. Disrespect toward the other parent will be played out by the child. It’s important for a child’s healthy development to have respect for authority figures, including both parents.

3. Observe appropriate boundaries. When it comes to your kids, it’s sometimes difficult to tell yourself what they’re doing with the other parent “is none of my business.” But if an activity won’t harm them physically or psychologically, it probably is none of your business. Recognize it’s okay, maybe even good, for children to learn different ways of doing things. It’s almost certain that the other parent won’t do everything your way.

4. Communicate regularly with the other parent. There’s lots to share. When children are small, the other parent needs to know the basics when parenting responsibilities are being transferred. Has the child eaten? Gone to the bathroom recently? Does he or she need more sleep or a bath? When children are older, both parents need to know about school activities, sports events and trips out of town. It’s good to get into a regular habit of checking in with each other on the days when parenting is shared. A worst-possible scenario is that lack of communication could lead to a child not being picked up after school or day care, or important medical treatment being disrupted.

5. Demonstrate positive conflict resolution. Don’t try to hide conflicts when they arise. Children generally know more about what’s going on than we give them credit for. Use conflict as an opportunity to show kids how to resolve issues in a responsible manner. Paul puts it this way: “Don’t step into the ring without taking time to cool off.”

6. Share with your co-parent what you need from him or her to do a good job of parenting. In our case, a regular schedule is important to Paul. He likes to know he has time he can count on with his son, Frequent schedule changes are disruptions he finds particularly irritating, especially when it involves “telephone tag.” I like to know I can depend on Paul to pick up Nick when he says he will. Everyone has different requirements for support. Be sure to be clear with the other parent about yours, and take time to inquire about his or hers. In our experience, guessing hasn’t been very productive.

7. Don’t allow all of the parenting tasks to fall to one parent. Typically, things that are out of balance don’t work well. Work at sharing parenting chores as equally as possible. Don’t hoard tasks and act like a martyr, and don’t expect the other parent to be in charge of all of the communicating, all of the extra purchases for your child or all of the discipline.

8. Be consistent - to the extent possible – in disciplining, feeding and caring for your child. This makes transitions from one household to another easier, thus minimizing the outbursts from children after visits with the other parent. Respect each other’s parenting approaches, and recognize that while consistency is optimal, differences are okay. Children are able to distinguish that something that’s okay at Dad’s house may not be okay at Morn’s, not because one parent is bad or wrong, but because the two parents are different.

9. Help your children recognize the other parent with appropriate gifts or cards. These express your children’s sentiments and make them feel good about themselves when they’re praised for their thoughtfulness. Take the time to help your children make or pick out holiday and birthday gifts for the other parent. Recognizing Mother’s and Father’s Day are particularly important because other relatives aren’t involved in celebrating these days.

10. Don’t punish your in-laws by keeping your kids from them after a divorce. Your in-laws are probably as disappointed as you and your former partner about the dissolution of your relationship. Grandparents can be a child’s greatest cheerleaders; don’t hurt your children and yourself by cutting off visits with them. In many cases, grandparents also provide back-up child care; this-isn’t something any single parent should give up willingly.

***my addition*** 11. Treat your ex's significant other with respect, and encourage your children to do so as well. You do not have to love or like this new person. However, they are now an authority figure and caretaker in your childrens' lives and everyone, especially the children, will adjust much easier if you treat your child's stepparent with civility and respect. If you have an issue with something the stepparent is doing, you should communicate this to your ex and his partner when the children aren't in earshot, and phrase your concern respectfully.