All communication, no matter how trivial, should be done in writing. Email is preferable to text because email is easily searchable and can be accessed from a variety of different devices.
Commit to your parenting plan
Follow the tenants of your parenting plan. Treat your parenting plan like a contract and abide by it to the letter and spirit. Do not make alterations except in emergent situations. One of the best ways to avoid conflict with an ex spouse it to steer clear of unpredictability in your interactions. In a situation with mutual respect and healthy communication, you may be able to ask your ex spouse to alter the schedule to accommodate an occasional calendar complication but it is best to treat your parenting plan like you would a job contract and plan your life accordingly when dealing with a high conflict ex.
Do not involve the kids or other family members in your drama
Comments like “things would be easier if your mother wasn't so difficult” or “your father always gives me trouble” do absolutely nothing positive. They might be cathartic for you, but they are damaging to your kids and undermine any steps you've taken to have better communication with you ex.
Treat others the way you want to be treated, even if they don't deserve it
You cannot control other people's behavior but you are entirely in control of your reaction to this behavior. Being the bigger person or the more mature communicator can feel burdensome but it is good for your karma and sets a great example for your children. Behaving in a respectful, fair, and considerate manner is not something you will look back and regret, even if it does not advance your position with your ex. Though it's often hard to remember in the heat of the moment, expending negative energy towards someone is in no way less taxing on your psyche than being kind.