A rub is a mixture of herbs, spices, and seasonings liberally applied to coat the outside of meat, poultry, or fish. Salt is always a great starting place for a rub. It helps the rub penetrate, and it rounds out and brings together the flavors of the ingredients. Sugar is also a popular addition to rubs as it caramelizes when exposed to high heat. If adding a sugar, do so sparingly as they burn easily. If using seeds, nuts, dried herbs, or spices, be sure to crush them first to release their entire flavor. The only real rule is that there is no right or wrong mixture. It's all a matter of personal preference!