Throughout your child's life, you and the other parent will have to make decisions based on what you feel is best for them. When you have gone through a divorce, there is a chance that you and your ex won't agree on what the kids need. This is a tough spot to be placed in, but you should remember that how you behave in these times can impact the future of your parenting relationship.
No matter how heated things are getting, you should always make sure that you are remaining respectful. This can be a real challenge, especially if your ex knows what buttons to push to get you heated. Always be willing to take a step back to evaluate the situation before deciding what to do. This might give you a chance to come up with a response that won't be deemed disrespectful.
You should also remember that everyone is going to make mistakes. You will make some and your ex is going to make some. Instead of holding those mistakes against your ex, be willing to forgive. There is a chance that you will need to help correct issues caused by the errors. Do this without trying to make your ex feel bad. You never know when you will need their help to move past a mess up that's your fault.
Even if your ex is hard to deal with, never keep the important points of the child's life from them. Relay all messages in a timely manner. For example, if you know the date of kindergarten graduation the day school starts, don't wait until a week before the event to tell your ex.
In all custody cases, the court order can help you find out what needs to be done. Schedules and terms of the parenting plan are all contained in the court file.