Light is critical. Don't grow indoors unless you can get it right. After light, proper soil is the next most important factor in producing healthy herb plants. Herbs require excellent drainage, especially during the winter months, when transpiration rates are lowest. When roots are confined in a pot or planter, water and air cannot move easily. To improve drainage without sacrificing nutrients, add sharp sand or perlite to a good sterilized compost mix. Most herbs which are of our interest do well in soils of a range pH 6 to 7, so try hard to stay in this range and you should see rewards. Flavours are stronger when herbs such as fenugreek and fennel grow outdoors in gardens. But in the confines of a pot, supplementary feedings with liquid fertilizer or organic fish emulsion are necessary. Feed herbs once a week when plants are actively growing, but not when dormant. Watering is not a trivial matter with herbs. In general, water less often and more thoroughly, and only when the soil is actually dry. When the soil is dry to the touch, add water until it comes out the bottom of the pot. If the water doesn't come out, then the pots have a drainage problem.