Swimming organisms provide examples of efficient movement through strategies such as reducing drag with specialized surface structures, taking advantage of tail flexibility, optimizing their swimming kinematics, and harnessing energy from flow patterns created by nearby swimmers. Understanding the strategies behind these high-efficiency swimming behaviors is invaluable across biological studies, fluid mechanics, and engineering. In this chapter, we present several primary strategies that are used either by individual fish or by fish schools to enhance swimming performance, especially those identified based on studies utilizing cutting-edge methods like theoretical analyses, computational fluid dynamics (CFD) simulations, and bioinspired robotics. These studies not only offer valuable hypotheses for biological research but also inspire engineers in the design of efficient underwater vehicles.