Decorate with: Star tip 16 and medium consistency icing. Hold bag at 45° at 3:00 (9:00 for lefties) with tip lightly touching surface.
Steadily squeeze and glide tip along the surface in an up and down motion.
Continue piping up and down with steady pressure. To end, stop pressure and pull tip away. For more elongated zigzags, move your hand to the desired height while maintaining a steady pressure. For a more relaxed look, increase the width as you move the bag along.
Hint: When piping zigzags, think about two motions simultaneously. The movement of your arm determines the height of the waves and the distance between them. The pressure on your bag determines the thickness of the line. Strive for uniform thickness and even spacing as you go.