Rule No. 1: Don't Hash It Out in the Moment
Nothing says "united front" like stepping into the metaphorical boxing ring with your partner to duke out whether or not your spectating toddler can have yet another piece of cake. Unless the decision is urgent and highly consequential, one of us will take the reins in the moment, then we'll discuss later how to handle similar situations in the future. This makes our coparenting conversations more productive and calm and helps us avoid turning each other into "the bad guy" in front of the kids.