Just because the leaves withered away doesn't mean that the sticks are dead. To test this, scrape a little bark away near the cut and see if there's a layer of green underneath the bark. If there is, the stick is "alive" and can still be propagated, under proper conditions. This is because most of the cutting's energy is stored in the sticks, not the leaves.I know of one nursery which removes all of the leaves and roots only the sticks!
The method I learned is to leave about 5-6 mature leaves on the cutting, pinch off any green new growth, and remove the bark and green layer for about an inch down to the end of the stick. Be sure to scrape off all green material. If the cutting has large leaves, you can take scissors and trim the leaves by 1/2 to 2/3. If your cutting has a long stem, it can be divided up into several sticks. For rooting medium, you can use Perlite, Vermiculite, composted pine bark, or filtered cypress mulch. I use aspirin-water (one original Alka-Seltzer tablet per gallon water) as a rooting hormone. Keep the medium moist, well-drained, not saturated. Then the most important thing is heat (70 + degrees) and humidity. Mist the leaves and then place the potted cuttings in a sealed clear bag. The bag should be placed in bright light but never in full sun. Crotons vary greatly in how long they take to root. Under ideal conditions, most take 4-8 weeks.
Don't try to root cuttings in water. The roots you get are generally too weak to make the transition from water to soil. Good Luck!