Adding complexity and details to your robot drawings can make them more visually appealing. To achieve this, focus on texture and precision. Use hatching and cross-hatching techniques to create the appearance of metal surfaces and shadows. Experiment with various shapes and sizes of mechanical parts to add intricacy to your robot's design. Additionally, consider adding fine lines for wiring, buttons, and small details. Don't be afraid to reference real-world machinery and technology to inspire your designs and ensure they have a sense of authenticity and depth.