A huge jar of oregano is economical only if it still tastes of oregano when you reach the bottom. For an occasional cook, a smaller packet can be the more useful purchase.
Keep dried herbs sealed and away from the steam rising from the stove. Tip a little into your hand or a spoon rather than shaking directly over a bubbling pan, where moisture can enter the container.
Rub a pinch between your fingers and smell it before cooking. A faded herb may contribute little, even when you double the amount. Fresh herbs are not always an exact volume swap, because their strength and water content differ. Use a recipe as a starting point, then taste the dish rather than pursuing a rigid conversion in every situation.