Take a lunge stance position: one foot forward with the knee bent, and the back knee an inch or two away from the ground. Shoulders should be slightly in front of hips.
Jump up, extending both legs.
Switch legs in midair, bringing the back leg to the front and front leg to the back.
If you're a beginner, don't switch legs in midair. Instead, start in a standing position with feet together, then jump and land into a lunge. Then jump back into standing position. Alternate legs.