Turns start from the skis up, which means your ankles, knees, and hips are the joints primarily responsible for turning your skis. And while it’s easy to focus on the action of your lower body in moguls, don’t lose sight of what your upper body should be doing. It should be strong and stable, but it should nevertheless be moving down the fall line.
To practice this, try Glen Plake’s “Stick and Rip” drill. Here, you’ll practice side-slipping from bump to bump, allowing your skis to briefly “stick” to the top of the mogul as your body keeps moving forward, eventually “ripping” your skis off the snow—like peeling apart Velcro.