Introduction: BBQ Brisket on a Smoker. I will show you how to do a low and slow BBQ Brisket.  
What you will need:
Brisket- preferably in the 8 lb range.  You can cook one of those monster 15 pounders, but it will take 15 hours or more.  
A BBQ smoker
A simple brisket spice rub
Yellow Mustard
An instant read thermometer
3 cinderblocks and a grill grate (for starting charcoals)
charcoal (a few matchlight type or lighter fluid, and regular charcoal)
Time to maintain your smoker at correct temperature for at least an hour per pound of brisket
Note: I should explain that in several of the pictures there is a brisket at the top of the frame, and 2 pork spareribs at the bottom of the frame.  Because I was cooking a small brisket (that I wanted) there was room on the smoker for ribs (which my wife wanted) Step 1: The Spice Rub. On a brisket, there are 2 layers of fat.  One runs through the center of the brisket, and the other covers the top.  You will need to trim the top cover of fat to about a 1/4 inch.  Put a light coat of yellow mustard all over your brisket and coat with the spice rub.  Just coat it, don't rub it.  Everything else I smoke is left overnight with a spice rub.  Brisket takes on flavor quicker than pork or poultry.  Take it out of the refrigerator, trim, add spice and let it sit at room temperature for an hour while you set up your smoker.
Here is a simple Brisket rub:
3/4 Cup Kosher salt
1/2 Cup Garlic powder
1/2 Cup Onion powder
1/2 Cup Italian Seasoning
This is way more rub than you need for this recipe.  Put it in a jar, mark it put the rest away.
DON'T PUT SUGAR IN THIS ONE!  The brisket I'm doing for the instructable here is only about 4 pounds.  I usually do an 8 lb brisket and so it is on the smoker for at least 8 hours.  Sugar will turn into an almost hard candy shell over your brisket.  Pepper burns and turns bitter when you cook it that long.
Put a light coat of yellow mustard Put the brisket on fat side up.  You won't be moving it for the duration of cooking.
Note:  the meat you see below the brisket are ribs.  I did both together as they cook at the same temperature and the same time because this is only a 4 Lb brisket.   Step 2: Heat Management. Beef Brisket is probably the most difficult BBQ you will do.  I say difficult but follow a few secrets, and you can turn brisket out like a pro.
These are the secrets to good BBQ Brisket.
1) Keep the heat at 220 degrees( F).  You can go up to 225 degrees while you make adjustments, but you should be cooking at 220 (F).  For you lucky people out there with top and bottom vents on your smokers this control is pretty easy.  After you load the charcoals in to the fire box, the bottom vent regulates how hot the coals will burn.  A wide open bottom vent will make the smoker hot.  Shut down the air to the coals and the smoker cools down.  The top vent controls how much smoke flows over the food.  Wide open, a lot of smoke.  Almost closed, a little smoke.
2) To be tender, the finished brisket should be at 190 degrees.  The time it takes to get there can vary according to variables such as outside temperature, your smoker,  rain, wind, etc.  It will take at least an hour per pound, so start your checks at that point.  It can take as long as an hour and a half per pound.  Don't get discurraged, it will be awsome when it does hit.  
If you don't have an instant read thermometer, you should get one.  They don't cost a lot and you can be sure when your meat is "spot on". Step 3: Charcoal Brickettes. Initially, I load my smoker up with 32 brickettes.  To start the coals, I usually put 4 "matchlight" type brickettes in the bottom of each hole in the cynderblock with a paper fuse, fill the balance of the holes with regular charcoal and light them up.  This week I didn't have ant "Matchlight", so put 4 regular charcoals in the bottom and added a little lighter fluid to them and continued as normal.  I like the assurance that the coals will light, but not the taste of fluid, so this lets me add a minimum of fluid.
Make sure you have water in the water pan.  Because I don't have adjustment vents on my smoker, it helps keep the smoker at a low temperature. 
You will have to add about 16 new brikettes (already white ashed) to the fire box every hour, so you need to start them about 15-20 minutes ahead of time.  Every hour when you replenish the charcoal, check the water pan to see if you need to add more.  Do not let the waterpan go dry or the temperature will soar.  
You will have to keep this up for at least an hour per pound of brisket, so think twice before buying the 15 lb monster.  It's better to buy (2) 8 pounders. Step 4: A Finished Brisket. I had what I feel was ideal BBQ conditions this weekend.  It was in the low 80's, with a gentle breeze.  
To my surprise my 4 pound Brisket was done in 4 hours.  190 degrees.  I put the brisket in a bowl and tightly covered the bowl with aluminum foil to rest for 20 minutes before slicing.
It came out perfectly.  Juicey and full of flavor.
Here is a slicing tip.  When you are going to slice, turn it fat side down and cut across the grain.  The knife with start better and your slices more uniform.  I did have a picture of the sliced brisket but it didn't save.  (Murphy's law)
Even my friends who like BBQ sauce eat this as is.  It needs nothing.