Best practices for refrigerant charge optimization in HVAC system maintenance include using the correct refrigerant type and amount, following manufacturer guidelines, and regularly checking and adjusting the refrigerant charge. Additionally, technicians should ensure that all system components are clean and free of debris, and that the system is properly evacuated and leak-tested before charging. By following these best practices, technicians can ensure that the HVAC system operates efficiently and effectively, while minimizing energy consumption and environmental impact.