1/2 cup brown sugar
2 tsp garlic powder
2 tsp onion powder
2 tsp salt
1 tsp black pepper
2 tsp cumin
I just created this rub myself today to use while grilling beef ribs and it was very yummy. I only rubbed it on the ribs about 3 or 4 hours ahead of time, but it would have been much yummier if I had done it the night before.
(And, FWIW, the trick apparently to grilling ribs is to have a fire that is not too hot and to spritz them with water or very water down barbecue sauce every so often throughout the grilling time. As long as your fire isn't too hot and you keep spritzing the ribs, the longer you grill them the more tender they will be.)