Triboelectric nanogenerators (TENGs) generate electricity through contact electrification. However, the output power is limited by several factors across materials, device design, and mechanical systems. This article aims to analyze several strategies for enhancing the outputs of TENGs across four key aspects: (1) The fundamentals of charge generation to establish effective strategies for designing or selecting tribo-materials, including recent practical approaches to surface and bulk modifications; (2) structural designs that maximize TENG output; (3) the output enhancement strategies tailored to different types of mechanical energy for practical applications; and (4) mechanical systems that effectively modulate external mechanical energy to increase TENG output. Finally, we provide a future outlook, highlighting open opportunities and remaining challenges for TENGs.