this is an art and each person does it a bit different, but there are basics to know.
The first is what you think is enough, will not be.
Properly cooked brisket is consumed and eaten and sought after.
Temperature is truly important - i prefer to do a 180 to 200 F cooking temperature...the last briskets i did stayed at that temperature for 24 hours and was by far the best i have made.
i put a rub on the brisket for 24 hours before it is cooked. What is in the rub is really up your tastes buds, BUT you need to insure items that will have the taste you want when they are slow cooked.
I use a blend of salt, sugar, hot pepper, paprika, garlic and black pepper. This does not reach far into the meat, but gives a bite to it as you sink your teeth into it.
Because this is slow and low, i can use garlic. If it were a high heat the garlic would add bitterness. I do not use fruit - i reserve that for pork, chicken and salmon.
The wood that is used is also discretionary and usually has to do with the part of the country you are from. Remembering this, know that fruit tree can give a sweet smoke, nut trees give a stronger, harsher flavor. Do not use evergreens!
With my wood smoker, i had trouble maintaining the correct temperature without constant supervision. I was talked into getting an electronic smoker and the temperature is well controlled.
The heat though MUST be moist. A tray of liquid between the heat source and the brisket is essential. I tend to just use water, but others use apple juice, wine and any number of non flammable other liquids
After 12 hours of cooking, you should wrap it so it does not lose moisture.
Save the juices that drip into the pan and make a dipping sauce or a gravy if you wish.
Finally, after it is out, you must let the brisket sit a cool a bit before it is cut.
This is artistry in the cooking world...enjoy!