For quick reference, a good rule of thumb is to substitute one teaspoon of crumbled dried , or 1/4 teaspoon powdered or dried herbs for each one tablespoon of fresh herbs called for.
Bay leaves are the only exception to most substitutions. Since they lose much of their flavor when dried, you should replace one fresh bay leaf with two dried bay leaves.
Most herbal flavors and aromas are released by heat. Although fresh herbs are usually preferred, dried versions can be used.
When possible, grind whole spices in a grinder or use a stone mortar & pestle just prior to using for enhanced flavor.
Toasting or dry roasting whole spices in a dry skillet over medium heat before grinding will bring out even more flavor.