Learn A Different Language
They need to be able to communicate with the engineers and designers in a way that instills trust and a belief that the PM knows what they’re talking about.
( Source: The Next Web | Product Managers: Who are these ‘mini-CEOs’ and what do they do? )
I am not a product manager - PM is a project manager in my world - but this ability still rings true. Learning how other folks see the world and how they describe their roles is imperative to executing product / project deliverables on time and with the right focus.