When I mix up a batch of dry rub, I leave out the salt. I have been taught that it is better to apply the salt by itself, so that you can measure the correct amount of salt per pound of meat -- as opposed to putting it in the rub, since the amount of rub you use is based on the amount of exposed surface area of your meat. It also means that you can opt to "dry brine" certain meats by applying the salt only, and letting the meat rest uncovered (but in the fridge) for some hours.
I usually go with half a tablespoon of coarse kosher salt per pound of beef.