1. Act like Adults
Yes, you are mad and hurt, but putting the other person down will get you nowhere. It is something immature people do out of spite, and you must be above all of that.
If children are involved, this advice is absolutely crucial. Putting your spouse down in front of your kids will just confuse and hurt them. They are already stressed by their parents splitting up and having custody battles over them. If you lowball your ex it is just going to add more unnecessary drama to what is already going on.