First, it is important to compartmentalize your emotions. Rather than allowing your history to dictate the way you speak with your ex, focus on your need to make decisions together without excessive conflict. One approach is to view your new relationship as a business partnership in which your business is to successfully raise your children. When you can see each other as co-partners, you both immediately have a stake in functional communication. You may still not respect, like, or trust one another, but at the very least you are united by the same goal: healthy, happy children who know their parents love them more than they love fighting.
Naturally, one of the problems in business relationship made up of only two people is that there is no tie-breaking vote. This is doubly difficult when you may have very different parenting styles, such as when one parent is viewed as “permissive” and the other “rigid.” However, “different” does not mean “wrong.” In fact, different styles, different points of view and different ways of doing things can all lead to children that have a richer range of skills. Instead of getting stuck on whose idea is “best,” recognize that neither partner ultimately knows what will work out best. You’ll need to pick one and know that you can always revisit the decision.