For most recipes, unless otherwise directed, mince herbs into tiny pieces. Chop with a chef's knife on a cutting board or snip with a kitchen scissors. To speed cutting with a scissors, cut herbs coarsely into a small bowl or cup and snip back and forth with your scissors. Some recipes may direct you to cut large leaves, such as basil, "chiffonnade-style" or into thin strips. An easy way to do this is to stack several leaves (about 3 to 5), roll into a tight roll, then cut into thin (1/16 to 1/8 inch) strips with a sharp knife.
While some recipes call for a sprig or sprigs of herbs, normally the part of the herb you harvest will be the leaves. For herbs with sturdier stems, such as marjoram, oregano, rosemary, sage and thyme, you can strip off the leaves by running your fingers down the stem from top to bottom. With small-leaved plants such as thyme, you can use both leaves and stems for cooking early in the season. Later in the season, as the stems become tougher, use just the leaves. For herbs with tender stems, such as parsley and cilantro, it's OK if you snip some of the stem in with the leaves when you're cutting these herbs.
Be careful if using a food processor to cut herbs -- it's easy to turn them to a paste rather than tiny pieces.