I do a lot of brisket. It takes some practice to get it right. There is some good info
here, but I disagree on some points. Here's my two cents:
Using foil, otherwise known as the Texas Crutch, is no sin. In fact, some prize winners do it all the time. Brisket can only really absorb ~3-4 hours of smoke (depending on the size of the brisket). After that, I loosely wrap it in foil and allow it to cook. If time is short, I can always finish it off in the oven.
I also use Worcestershire sauce
first, then mustard, then a dry rub. I use a standard BBQ rub, but
first add an extra amount of fresh cracked black pepper. Wrap the prepped meat in plastic and refrigerate overnight. Allow it to come to room temp before placing it on the smoker. I also use pellets instead or wood and use a drip pan for those first few hours, but that's personal preference. After it has gone for a few hours, I'll spray it with apple juice from time to time to keep it moist and give it a nice sheen.