Hoya cuttings can be propagated in any of the following three ways:
1. Submerge the cut end in water. Keep out of direct sunlight and refresh water occasionally as needed. Replant when at least 1" of roots have grown.
2. Stick the calloused ends of the Hoya cuttings in well-draining soil. Keep out of direct sunlight and do not water for a couple of weeks. Once the plants start to shoot out roots, you can start a regular watering cycle.
3. Submerge the cut end of the Hoya plant in a mixture of water and lyca (clay pebbles). Refresh the water occasionally and replant, along with any clinging pebbles, once at least 1" of roots have grown.
Method #3 seems to be the fastest in our experience, but all three methods work.