You hear “letting go” a lot to reduce tension in the body. Also, “let the qi flow,” which is not heard as much. The how to do either is even less known or understood. One key: find the tension, become familiar with what tension is. Begin simply seeking tension, clenching, holding back, hesitation, and pain (of course).
Move through it
Not just moving it, the part that is tense, but moving “through it.” What is moving? The joint, muscle, even bone, etc., but also energy flowing—a feeling beyond mechanical motion of the body material. It permeates flesh and bone, and travels like the wind rising up from the river’s current.
Energy has no shape except what is expressed by its motion through space. Water is similar in its behavior. If qi flows naturally, then we have only to learn to open the pathways so it may travel.