A Power BI development company should prioritize clarity and usability in data visualization by adhering to best design principles. Understand the client's goals and KPIs before selecting chart types. Choose visuals that best represent the data, avoiding clutter and ensuring that the dashboard is easy to navigate. Use colors strategically to highlight important trends and patterns, and maintain a consistent layout across all reports. Implement drill-down features to allow users to explore deeper insights without overwhelming them. Testing the visualizations with end-users ensures that the reports are delivering actionable insights and are user-friendly.