Just root it like any other green/softwood cutting .. make the cutting about four to 6 inches long, remove the lower leaves and any buds or flowers on the top and stick it in some soil making sure a leaf node is under the soil. You want to keep the soil moist .. more on the dry side than wet side.
You can also take cuttings and put them in water - some plants will root this way.
Once it roots, you want to remove any buds that form until it has had time to make a good root system. Flowering take a whole lot of energy out of a plant and it's better for that energy to go into making roots and leaves rather than flowering.
