As far as rub is concerned. For brisket I go half parts each salt and pepper (two tablespoons) tablespoon garlic powder (not salt), couple of tea spoons either chili flakes or chili powder. Simple.
Sauce is where it's at though. I use asian inspired technique. Salt, sweet, tangy, heat (spice), umami.
So in a sauce pan over low heat stir together half cup water, half cup ketchup, 2 tablespoons apple cider vinegar, tablespoon yellow mustard. Add a quarter cup brown sugar, tablespoon worcester sauce, teas spoon salt, tea spoon pepper, tea spoon cayenne pepper or your favorite chili flake or powder to taste. If it needs thickening up use a tea spoon of cornstarch mixed with a little bit of water. Will also give it a silky consistency. Taste the sauce on a piece of brisket. If too sweet add a little more vinegar or lemon juice. If too tart add more sweet. You need to find a balance there. tasting is the key.
Brown sugar won't give it a ton of sweetness, it will just bring everything together. Can also use honey.