When experimenting with new rubs, it is important to keep salt out of the mix until it can be used to enhance flavor instead of defining it. Doing so in previous steps would compromise the integrity of new flavors and ultimately the finished product. Once the rub is finished, however, the key decision is how much salt should be introduced. "How liberally do you want to use the rub?" says Mays "If you want to use a lot, you'll just add a little salt. If you use only a little spice, you'll want to use more salt."
He also encourages experimenting with different kinds: "Maldon, fleur de sel, Himalayan salt. Each one has a different minerality to it." Go around your kitchen and actually taste the various types of salts you have before adding to the mix. Salt isn't just salty.