Summarize:

While not all knuckle-ballers take this hop-step, it is incredibly helpful to keep the ball from spinning, especially on free kicks. Think of it as a slight scissor kick. If you're kicking with your right foot, you'd approach and place the left near the ball. As your right leg comes down, pull your left foot up and back, leaving your torso up to stay balanced. You then kick the ball and land on your right foot, placing it almost where the left was. You'll look like your running in place, or snapping your feet past each other like a broken set of scissors. Many players want to go out, learn the knuckle, and start ripping pro-level free kicks in the same afternoon. Most of those players won't be able to do it. Instead, start learning with a simple 1-step run up, only 10-20 yards away from the goal. Work on a comfortably plant foot distance and resisting your follow-through motion. The ball may not zig-zag much at this speed, but you'll be able tell if it is spinning or not. Once you can hit the ball without spin it's time to move on to full strikes. You want your kicking motion to be as economical as possible. Your plant foot and torso should be set comfortably, with your ankles and knees slightly bent. Your run-up should be well-contained and calm, without lots of twisting, moving, or adjusting. Your kicking leg needs to be strong from quad to ankle, without excess movement. Think about straight lines -- any curves or excess side-to-side movement makes it more likely you hit the ball at an angle, causing spin. Aim to strike with the bone on the inside-top of your foot. The bone in between your laces and instep is the hardest area of your foot. You can feel it with your hand, running from your ankle to big toe. Once you have the basic kick down, work on turning your ankle out slightly to make contact with this rock-hard bone. However, you must keep the rest of your shooting motion straight, hitting the ball in the dead center. No matter how easy and effortless he makes it look, Gareth Bale is the first to admit that the shot took years to perfect. His advice? Start shooting on an open net, then add mannequins or a wall in front of you. Finally, add a keeper to work on accuracy. Above all, hit a few knuckleballs every day, focusing on perfecting the technique so that it becomes second nature.
Practice the hop step without a ball. Don't worry about power until you can hit the ball without spin. Keep your body compact, still, and strong. Turn your foot out slightly for added power. Practice the shot daily, adding challenges as you grow comfortable.