Treat unit tests like they are production code - in terms of their quality, standards, and maintenance.
Unit tests provide the path to production in the form of a quality gate - therefore if tests hinder getting changes to production, through being ridden with Technical Debt, or by not clearly communicating the intent of the code, then the ability of the developer to deliver to production is compromised (Speed is a byproduct of quality)
By listening to tests, a developer can identify improvements that can be made to test and application code which will improve the overall quality.