Think of spice rubs as dry marinades. Standard dry rubs typically contain 4 parts each salt and sugar, 3 parts pepper, such as cayenne or ground black, and 1 part transition spice -- a spice that marries the salt and sugar with the protein -- and 1 part spice of choice. The exact proportion of sugar varies with the protein; for example, pork does best with more sugar than does beef. What doesn't vary, however, is application; the goal of a spice-rub application is full coverage, and then some. The "then some" forms the prized crust well-spiced foods are known for.
Take the protein out of the refrigerator and let the surface warm to room temperature, about 15 to 30 minutes, depending on size. Mix the spice rub a final time and transfer it to a spice shaker.
Trim off any extraneous or hanging fat from the protein. If applying the spice rub to skin-on poultry, loosen enough of the skin to pull it 1/2 inch away from the flesh. You can also puncture the skin several times with the tines of a fork.
If applying the spice rub to skin-on fish, make vertical slashes through the skin at 1/2- to 1-inch intervals.
Set the protein inside a shallow dish or on a larger plate or tray. Hold the spice shaker 3 or 4 inches away from the protein and sprinkle the spices over it in a uniform manner.
Turn the protein over and hold it as needed while shaking the spice shaker to cover the entire piece uniformly. For hard-to-reach areas, such as under the poultry skin, lift the skin away from the flesh while shaking the spice shaker. Apply the spice rub all over the protein a second time to achieve heavy coverage.
Position a piece of plastic wrap on the work surface; the plastic wrap should measure 3 or 4 times the width of the protein. Set the protein on one end of the length of plastic.
Wrap the plastic as tightly as possible around the protein. Position a second piece of plastic wrap on the work surface; this piece, too, should be 3 or 4 times larger than the protein.
Wrap the protein as tightly as possible a second time; this time, however, wrap the protein in a direction perpendicular to the first direction.
Set the wrapped protein in a shallow dish lined with a few paper towels and place it in the refrigerator. Let the protein stand in the refrigerator for 30 minutes per pound.
Unwrap the protein; let it stand at room temperature for about 1 hour before cooking.