Herbs do not require a rich soil, but the soil must drain well.
A good soil blend is to add equal parts of topsoil, sand and compost. Make sure your plants receive at least 5 hours per day of sunlight.
Each spring, as you prepare the garden for planting, incorporate organic matter into the soil by tilling or turning it under with a spade. Organic matter is material that was once living but is now dead and decaying. You can use such materials as ground corncobs, sawdust, bark chips, straw, hay, grass clippings, and cover crops to serve as organic matter.
Your own compost pile can supply you with excellent organic matter to enrich the soil.