Developers should write clean, efficient, and maintainable code in both DAX and M language to ensure better performance and readability. This includes using consistent naming conventions for measures and calculated columns, avoiding overly complex nested DAX formulas, and leveraging variables (VAR) for reusability. In Power Query (M language), Power BI developers should reduce the number of transformation steps, avoid unnecessary row-by-row operations, and use buffered functions to enhance performance. Additionally, documentation and inline comments should be added to improve code readability and simplify debugging. Optimized and structured coding improves Power BI solution scalability.