Wormriding is the art of riding a sandworm. Generally done by the Fremen, wormriding is usually done by prying open a scale from a sandworm and putting sand into it, usually with a maker hook. Irritated, the worm will turn to put the exposed scale upwards, not submerging its body until the scales were back in place. A prepared Fremen could then use the maker hooks to control the worm's lateral movement by attaching them to its mouth, pulling to force it to change direction.
In addition to all of this, one could also use a worm charmer to summon a worm and thus ride it. Sandworms even became a widely-used method of travel, long distances being measured in sandworms, the distance over which a sandworm would take its rider before becoming too exhausted and being allowed to submerge again.