You may be wondering what duck-diving actually is.Any breaking wave over approximately two feet requires that you duck under the wave rather than float over it. Thus, the term "duck-dive!" Honestly, duck-diving wasn't something I learned until I had surfed for a couple of months. Yet for sake of chronology, let's discuss this skill before we learn to stand up.
How to Duck-diveAs you approach an oncoming wave while paddling, try to have as much speed as possible. About two feet before making contact with the white water, grab both rails (side edges of board) halfway between the nose and midpoint of your board. Push all your upper body weight onto your hands and arms until you feel the nose begin to go under. Point your head down and let your body follow.
Once your body is just below the surface, bend your dominant leg and use that knee to push the tail under the water also. Your momentum should thrust you under the quickly passing wave and only require you to be under water for a short time. As the wave passes let the flotation of your board lift you to the surface. Now you have the skill to paddle to the lineup or to the next wave and duck under it.