This study develops actionable design principles for assessing data quality (DQ) when converting National Cancer Registry data to the OMOP Common Data Model, a critical step for improving the utility of Electronic Health Records (EHRs) in cancer research. By applying Action Design Research, the study identifies core data quality issues and addresses them through iterative, stakeholder-informed interventions. These interventions enhance transparency, automation, and interoperability in DQ processes. The design principles derived from these interventions support safer, higher-quality EHR use, contributing to a healthier society with reliable data-driven insights, especially vital for the societal transition toward data-informed healthcare.