Part of what "learning to be poly" was about for me was learning new ways of communicating that I just hadn't learned before. It involved working together to break down the walls that we put up ourselves - afraid to bring something up because it may upset them and so on. And it is most definitely a two-way thing - expressing a willingness to listen is as important as expressing a willingness to talk.
It's not easy, and at times it can be painful at the start, but once you get into the habit I have found that the rewards are amazing, because you are no longer second-guessing your partner.
It's not something that comes overnight, though, in my experience - it's a process of evolution of your relationship rather than a flicking of a switch. Part of it is talking about how you talk to each other and helping each other reinforce new ways of communicating. It's definitely a teamwork thing in my opinion.
"Listen, or your tongue will make you deaf." - Native American Proverb