After initially failing with cuttings from Coronilla, I consulted the propagator's bible, the RHS Propagating Plants*, and by following their instructions, I was successful.
The book recommends taking greenwood stem-tip cuttings in early summer, when the new growth is just beginning to harden up (although the Coronilla never gets really hard and woody). Take cuttings about 3-4 inches long, remove any flowers but leave the growing tips on. Insert into seed and cutting compost (I use Levington’s), cover the pot with a plastic bag, and keep moist. Mine took a couple of months before showing signs of life.
*The Royal Horticultural Society Propagating Plants, Editor-in-Chief Alan Toogood, published by Dorling Kindersley