This is a complex “walking” stretch derived from taijiquan, which I think is much more effective than conventional iliotibial band stretches (for whatever ITB stretching is worth).
The iliotibial band mobilization is a dynamic stretch that occurs as you are moving, teaching the muscles that control the tension on the ITB to be responsive, shortening and lengthening as needed. By “freezing” the movement in the right place, you can also stretch the ITB more powerfully than by any other method I know of.
Begin by standing. Step forward the distance of a normal stride, placing your front foot in line with your back foot or even slightly across the midline. The toe of the forward foot should be pointed outwards. The forward leg is not the leg you’re stretching—the back leg gets the stretch.
Crouch deeply, lowering the knee of the back leg almost to the ground. As you do so, push your hip (of the back leg) out to the same side, and your knee (of the back leg) to the far side. Then stand up, step forward with your other leg, and repeat on the other side.
Another important element of this mobilization is arm movement (not shown in diagram). It may take some practice to integrate this step, especially while moving. However, the stretch is strengthened significantly by reaching up and away from the stretch side. That is, when dropping the right knee and stretching the right ITB, reach upwards, backwards and to the left, leaning away from the front right corner of the pelvis.
Here’s a video of the stretch being doing mobilization-style (continuously moving in and out of the stretch, rather than holding it).
Good for …