You can choose to take hardwood cuttings later in the year but many find that they have more success with softwood cuttings which are best taken in May or June. This is a remarkably easy way to propagate shrubby herbs, though you should be aware that a 100% success rate is unlikely and that all your cuttings are unlikely to take root. Don't worry about it, just take a number of cuttings and if you get it right, some of them should work out.
To take a softwood cuttings, simply cut off a short stem less than ten centimetres long – look for healthy side shoots and cut off the stem just below a leaf node (where a leaf joins the stem). Cut at an angle to increase the surface area for rooting. You should ideally take softwood herb cuttings early in the morning as this is when the herbs will be at their firmest and freshest. It is best to take cuttings from a plant that has been watered just the day before. Remember to take more cuttings than you need to account for failures and get them to your potting area as quickly as possible.
When it comes to choosing a planting medium for your cuttings, you want something that holds moisture and yet will not be waterlogged. A mix of sand and compost usually does the trick. If you wish you can increase though not ensure the success of your cuttings by dipping the ends in rooting powder before you plant them, though this is not strictly necessary. It is a good idea, however, to clear the leaves from the bottom of the cutting so as to give each one the best chance.
Place your herb cutting in a warm and humid environment. Since the cuttings have no roots, they cannot replace the water they lose as they usually would do. Keeping the air around the cuttings humid will reduce the amount of water lost through the leaves before roots begin to form. You can keep a humid atmosphere for your herbs by covering the pots in which you sow them with cloches, which you can make by cutting the bottom off a drinks bottle and placing the remainder over the cuttings container. If all is well, herb cuttings should begin to grow roots in around three weeks to a month, though it can take longer. Keep the potting medium moist but not waterlogged throughout that time and remove the cover daily to reduce the risk of mould developing under your cloches.
It will be obvious when roots have formed because you will begin to see new growth. When you do see growth, you can take your cuttings and pot them up or transplant them to their final growing positions.