Safety around communication. That is, let people know it's safe to call you out, say no, set boundaries or ask for clarity on things. It amazes me how little thought many put into communication and its nuances, and forget to allow for projection/assumptions. Be clear and make sure the climate is such that others feel safe to be clear.

I realised the importance of this when a friend and I were having a convo about two other friendships we'd recently experienced where the response to any kind of boundary was defensiveness, passive-aggression or silent treatment. We realised there is value in letting those around us know they were safe to speak frankly, as we have all experienced the other kind if dynamic with someone, and that it causes so much unnecessary anxiety.