This drill looks simple and it is simple, but it teaches your hips mobility and control at the same time. Stand on one leg with core tight, and trace slow, deliberate circles with your other knee—forward, out to the side, back, and in. Start small, then gradually increase the size of the circle. Your standing leg stays strong and still, hips level. After several circles in one direction, reverse. The work lives in the hip that's circling and in the core that keeps you from wobbling. This isn't flashy, but it's foundational.