What are the overarching strategies or artefacts for improving UX of products

Not sure exactly how to phrase this question, but what would you consider overarching strategies or artefacts for improving UX of products in the long term. These would be maintained within team and serve as a overall guide that help make decisions when designing.

Some examples i believe that might be tone of voice guide, brand guide, visual direction, customer journey map.

What else is out there?