How did James Watt improve on the first steam engines?

James Watt significantly improved on the first steam engines by introducing a separate condenser, which allowed steam to condense without cooling the cylinder, thus increasing efficiency and reducing fuel consumption. He also developed a rotary motion mechanism, enabling the steam engine to power machinery, not just pumps. Additionally, Watt's enhancements included better insulation and the ability to control the engine's speed, making steam engines more practical and widely used in industry and transportation. These innovations laid the foundation for the Industrial Revolution.