Product design starts with designing the interactions of the people who will build it. The quality of teamwork will reflect on the product itself. If the goals, values, and processes of the team are not well designed, there's little hope that the product they produce will be any better.
Aware that your common sense worth only as much
as the information you are drawing on.
Objective in your assessments
and not mislead by false assumptions and preconceptions.
Able to communicate your solution in a manner
that it's going to be actually implemented.
Made sure that you are tackling the right problem in the first place.
Writing clean code is as much a UX problem as designing user interfaces. They differ in audience and medium, but the principles of usability need to be applied in both cases.