Select a cutting on the mother plant with two or three healthy nodes. Pinch off the leaf petioles (leaf stems) on the bottom node as close to the main stem as possible - this will be the main future rooting area - roots will be produced from this axial bud site and along the stem. The remaining one or two nodes above this point, with their healthy leafsets, will provide food via photosynthesis for the ensuing root growth below.
Within a short period of time, after these wounds have healed over, cut off the clone with a razor blade, knife, etc. about 1/2" or so below the bottom node, doesn't have to be done under water, just cut where it's convenient for you. Immediately dip the bottom node and stem in Rootone-F or a similiar rooting material which contains a fungicide, place into a rockwool cube or hole punched into the soil, deep enough to support the cutting while allowing for ample root growth in the near future. Close the hole with your fingers working the medium towards the stem, water to settle the soil around the submerged stem, and place in strong indirect light, providing plenty of humidity by whatever method you're comfortable with....misting, plastic bag, dome, etc. allowing some air exchange. Fresh air can be provided by taking a lit cigarette and burning a dozen holes in a large clear plastic bag placed over the cutting, or if you use a dome, by lifting the clear dome once in a while. Bottom line is, the cutting requires close to 100% RH. Common sense dictates that the plant has no means of water uptake and will incur moisture loss thru the leaves, so you must reduce excessive moisture loss by providing an environment of high humidity until roots start growing from the bottom node and the stem that had been placed below ground level.
The cutting will have droopy leaves and stems for a while, this is normal. As you see things perk up, pot up. Provide plenty of fresh air and don't expose to sun or strong direct light until you are sure you have a nice root flush, as that will only dessicate the cutting further.
Be sure to maintain sanitary conditions throughout the entire process, including sterilizing the cutting tool between cuts. Do not dip the cutting into the entire rooting compound; remove enough rooting agent from its original container to use for one cloning session.
Good luck,
Uncle Ben