You are actually better to raise from seed than taking cuttings. To be honest they are so cheap to buy that it is hardly worth doing either.

As Moongrower says they are very cheap and easy to grow from seed. On my nursery I grow 150-200 a year from two 39p packets of seed !

However aubretias do have quite a range of colours and some are nicer than others. If you want to get a new plant from an aubretia you particularly like just spread a bit of soil/compost over some shoots and in a few weeks they'll root into it and you can detach the newly rooted part from the parent plant.

Aubretias also self "layer" themselves so you may be able to gently pull an already rooted piece off the parent plant