Apart from herbs such as bay that are used whole, herbs are usually best prepared by picking the leaves from the stalks (although this is not always necessary), then chopping them as finely as desired with a chefs' knife or two-handled rocking knife (mezzaluna); alternatively, cut bunches of tender herbs such as chives into small pieces using kitchen scissors. Some tender herbs - particularly basil, tarragon and mint - bruise easily, a problem exacerbated by blunt kitchen knives. To prevent bruising and discolouration, avoid chopping these herbs finely and make sure you use a sharp knife. Alternatively, add the whole leaves to dishes, or tear them into small pieces with your fingers.
The volatile oils that give flavour and fragrance to the tenderest herbs dissipate quickly after exposure to heat, so it's best to add them to dishes towards the end of cooking, or just before serving. However, more robust herbs such as bay, sage, rosemary and common thyme are best when given time to meld with the other ingredients in the dish, so should be added during cooking. Tender herbs - such as basil, chervil, chives, coriander, dill, mint, parsley, tarragon - can also be used raw and make delicious salad ingredients.