1. Trying to win
When you are having an argument with your partner, you are not in a race, and one of you should be the winner. This is definitely one of the worst mistakes couples make after a fight.
There is no such thing as winning an argument. When this happens, you should let things sit for a while, and after everything is more relaxed, you can try to have a conversation with your partner about what happened.
This is the only way you can solve a conflict, and it will also help you learn more about one another. Trying to win a fight is solving nothing, and even more, it can make you and your partner grow apart from each other.
A fight is not a competition; a fight is a situation in which you and your spouse realize that you are different and that you should try to find a middle ground.