Every single post above is dead on and I have tried and love them all.
I usually like coarse ground pepper as well. I just use my pepper grinder set on coarse and grind however much fresh I need right onto the brisket. It takes a while, but the fresh ground pepper is worth it.
Also, the celery seed is a very nice touch that adds a rich flavor that I cant describe, but everyone always says the briskit tastes very BEEFY when I use it. Just be careful and don't use too much. It is like sesame seed oil. You can get too much of a good thing.
The only slight variation on top of these is:
I ALWAYS measure salt separately and per pound per hunk of meat. For brisket, shoulders and other solid hunks of meat I use 1/2 teaspoon of salt per pound AFTER trimmed.
For ribs and other hunks o meat with bones I lower that amount vs % of bones. For ribs that are almost half bone, I use 1/2 teaspoon salt per 1.5 - 2 pounds of meat leaning toward 1/2 tsp per 1.5 for the meatier back ribs.
I almost never use rubs with salt included or I make my own spice only rubs or just throw spices on as I go. The salt is the one spice that can have a huge effect on your result. Too much or too little have significant flavor and texture/moisture differences in the outcome. I consider salt not only a flavor but a chemical reaction and not just a spice. Ever since I have started measuring salt on every cook the last 4 years or so, I have had MUCH more consistent and balanced results. My neighbors and wife agree.
The other "top secret" of lots of competition and other chefs is MSG. This is an oddly controversial ingredient, but I have done tons of research and have been using it for years and I have done tests with and without it and I can tell you it does make all meats MOUTHWATERING. There is a reason all the Chinese restaurants tasted so good for decades and they still use it in Asia to this day. IT IS GOOD! MSG is found naturally in MANY healthy foods. It's called UMAMI!
I replace half my salt with 1.5 times MSG or as easily found in stores as the brand 'Accent' in the red and white container. So, if I need 2 teaspoons of salt. I actually use 1 teaspoon of salt and 1.5 tsp of Accent.
GAME CHANGER!