Good choices for a windowsill herb garden include basil, cilantro, dill, oregano, rosemary, sage and thyme. You can start herbs from seed or purchase small plants. Annual herbs are especially easy to start from seed; most perennial herbs take longer to germinate and grow so it's easier to start with plants.
Use individual pots for each herb so you can give each plant the specific care it needs. Be sure containers have drainage holes and waterproof saucers. If you want to plant multiple types of herbs in a single container, make sure they have the same cultural requirements.
If starting seeds, fill container with potting mix. Use a commercial seed-starting mix or potting soil, or a 50:50 combination of the two. Avoid using garden soil, which tends to be heavy and may contain disease organisms. Sow seeds, checking the seed packet to determine planting depth. Learn what conditions each herb prefers; for example, basil prefers warmth, while sage and rosemary like cooler temperatures. Consider choosing compact or dwarf varieties to fit your space.
Place containers in a sunny, south-facing window. A south-facing window is adequate for most herbs, although supplemental fluorescent lights will help in winter. To prevent injury to foliage, don't allow leaves to touch cold windows. Water your herbs to keep soil moist but not soggy, and drain saucers after watering. Fertilize every two weeks with a half-strength solution of an all-purpose fertilizer. Pinch back branching plants, such as basil, to keep them shrubby rather than leggy.