Choose a wood that will complement your dish, for their aromatic smoke has specific flavors much as spices do. Mesquite and hickory are famous for the barbecues of the American South and Southwest, while cedar and alder flavor fish in the Pacific Northwest. Apple offers a delicate, fruity aroma, and pecan imparts a distinctively sweet, nutty taste. Grapevine trimmings are especially popular for grilling in the Mediterranean. Dry, sturdy stems of woody herbs, such as rosemary, thyme, oregano, basil and fennel, add their distinctive flavors to foods.
For charcoal grills, first soak wood chips and herbs in water for 30 to 60 minutes so they will smoke slowly instead of burning away immediately. Scatter the wood or herbs directly on the hot coals just before placing the food on the grill.
For gas grills, fill the vented smoker box or a perforated foil packet with dry wood chips or herb stems and then place it directly over the heat element. Close the cover for a more intense flavor.