Progressions
There are a wide range of variations on this theme but the most important element is that the ‘core’ of your body (including the ‘core’ of your hips and shoulders) stays rock solid.
Each progression starts with the basic ‘hover’ or vertical movement and then increasing the difficulty by moving the opposing limbs in different planes. With any variation, move slowly and hold the end position for three to five seconds in the same way as with the basic exercise.