When the brisket is done smoking, letting it rest makes a lot of difference in improving juiciness. When the smoked brisket is done, wrap it in aluminum foil to trap the juices that'll continue to drip out. Then, what I like to do is to place it in a dry cooler, cover it with a couple of clean bath towels (to help trap the heat), close the cooler lid, then forget about it for two or three hours. The juices will have plenty of time to redistribute evenly through the meat.
Giving the brisket a half hour to rest will help, but I believe that more rest time makes a big difference in the final quality of the smoked brisket.
