Divorce. For some this transition is the easiest thing in life. Some people have waited for the day they were finally divorced from their spouse. For others, it's the most difficult thing they will ever endure. Divorce is a change, a huge change for everyone no matter if it's a happy occasion or a sad one for the spouses, when children are involved it can get very messy.
Many parents are guilty of one thing, talking crap about the other parent in front of the children. Stop it. Your children are one half of the other person. You might hate the person you have divorced, but respect the fact that your children still love that person. "Love your child more than you hate your ex-spouse". No matter how awful your divorce might have been, or even your marriage, repeat this to yourself often. It's very difficult to be the bigger person, but it's necessary for your child. You as the parents divorced for a reason. Even if the divorce wasn't mutual, or was for a horrible reason, there was likely conflict involved. Likely the children were a part of the divorce discussion. Likely you divorced so you as people could have a better life. Give your children that gift. Do not put them in the middle of constant conflict between the two of you.
If you must have conflict, don't do it in front of the kids. Choose a time when the kids are in bed and do not scream and yell. If you two can not get along for the sake of parenting your children and you need to have a discussion, do so in a text or an email. Sometimes tone of voice is the main reason for an argument. Sometimes just hearing your ex spouses voice is enough to make your skin crawl. You don't have to love your ex spouse, you don't even have to like them. You do have to be a good parent though. Both ex spouses have an obligation to their children to successfully raise them into adulthood.
Do not meddle in your ex spouses life. Quite frankly unless their new partner is a meth addict and cooking meth in his or her basement, it's none of your business who they are dating. While you might not think much of the person they've picked, unless the courts find them unfit, there's nothing you can do about it. Just accept that this person is now going to be in your child's life. If you talk badly about that person, and your child likes them, your child will grow to resent you. Maybe they don't parent the same as you, but that doesn't make them a bad person. They are not trying to replace you, nor will your child replace you with that person. Just be the best parent you can be when your child is with you. Just because dad's girlfriend fixes your daughter's hair, doesn't mean you should fight with them. Be thankful this person actually enjoys spending time with your child. At least your child is being cared for. Same goes for dads who get mad at mom's new boyfriend, so what if he takes your son fishing, at least your son is being cared for. You do not have to be best friends with the other person, just be civil.
Do not have your children call the new person in your life, "mom or dad". This is only OK if the child is very little and your ex spouse has basically abandoned them. If your new partner has raised this child from the time they were six months old, and your child is now 10, that person has become their honorary parent for the most part. If the step-parent is comfortable with this, as well as your child, by all means, go ahead. Otherwise you're just doing it to spite the other parent. This is not okay. Spite has no place in successful co-parenting relationships.
Work with one another. If dad wants to take your child to a baseball game on one of your days, and you want to take the child to a party on a certain day, switch. Don't keep the child from a fun time because you want to be spiteful. Perhaps dad can afford an activity you can't at the moment. Perhaps it's something your child really wants to do. Let the child go if it doesn't interfere with something important you already have planned. Maybe mom's family has a holiday party on one of your scheduled visitation days and she would like the child to attend. Work with her on this. If you don't already have plans, let the child go to the party, but only if mom lets you keep the child some extra hours to make up for the time spent away.
Don't look at the other parents gifts as a bad thing. What I mean by that is, one parent might out gift the other parent for holidays and birthdays. So what. Perhaps by consulting with the other parent on what they plan to buy for the child is actually a good thing. First off it's a great plan so you don't both buy the same things. Second of all, look forward to all the wonderful things your child will receive because you are a split family. Look at it as your child having a better holiday than if you were buying yourself. Your child will receive double the amount of holiday fun now. If your child comes home with a new expensive piece of clothing, simply say to them, "Oh I know you've really been wanting that, I'm glad you finally got it". Be happy for them.
Accept that not everything is in your control now. You both don't have to parent the same way. It's not the law. If your child is being cared for at both homes, don't turn petty things into huge issues. Perhaps your child eats canned food at dad's house and you feed only fresh organic food at your house. While you might think this is awful, at least your child is being fed. Maybe one parent sends the child in mismatched clothing, but clean clothing. At least that parent is providing a clean environment for the child. People aren't perfect. As long as a clean, safe, stable environment is being provided, don't sweat the small stuff.
Stop trying to save your image. Parenting is messy. No parent is a perfect parent. You might clean your entire home with bleach every day, your child might wear the best brands of clothing, there is still going to come a day when you mess up. Your child will forget their homework in their bedroom, or maybe even burn themselves on the stove, or even eat a booger when you aren't looking. No parent or child is perfect. Stop making the other parent feel awful when they aren't perfect either.
Children are going to try to turn you against the other parent. This is a famous defense mechanism for a child. They feel like they are in control in a crazy world when they do this. "Mom never plays with me", "Dad always goes out when I'm at his house". Stop buying into this. This ruins more co-parenting relationships than anything else. If you have deep concern, talk with the other parent. Even if they are doing something, they will likely deny it in fear of you flying off the handle. Honestly the only thing you really need to involve yourself in is if the child accuses the other parent of abuse, and there's evidence of this abuse. Even then remember, children can't always say what they mean to say. Perhaps your daughter comes home and says something to the effect of "dad hurt my butt". A sentence like that can make you jump to all sorts of conclusions. Perhaps the only thing that has happened is dad was holding your daughter, and she went to slip out of his arms, he caught her and it just happened to be he caught her by grabbing her rear. A perfectly innocent act has the potential to get a perfectly happy child removed from her dad. Or a really horrible set of investigations will happen, along with a lot of unwanted painful testing for the child. Just be careful what conclusions you draw from what your child is telling you.
Successful co-parenting relationships do not mean still loving or liking your ex spouse. They just mean you have to love your children. If successful interaction is impossible, do so through text or email. If you can't stand the sight of your ex spouse, choose a parent or relative to do child exchanges for you. When attending activities together, sit far apart. Still allow the other parent to give the child a hug and kiss or talk to the child at the activity. Children cannot thrive in stress. Being mean and nasty to the other parent creates stress for them. Always remember, "Love your child more than you hate your ex spouse".