My pops is a brisket cooking machine. I'll try to give some advice on this but since I've only cooked like 4 briskets by myself my entire life the info might be spotty but it should be a start.
1) Soak your wood chips. The more moisture the more smoke and the more idea the temperature. Also see if you can come across some actual logs if you can. Try to get your hands on some mesquite or hickory. Those two have the best flavor.
2) Use the charcoal just to get your fire started but just a little. After you have your fire going use the wood chips and keep the fire at a low flame with the wood chips alone.
3) The more smoke the better if you aren't choking on the smoke everytime you open up the pit it's not enough.
4) Cook it away from the heat and with the fat side up. The meat must cook slowly over a low heat to get the maximum flavor and tenderness.
5) THE most important...cook it as long as you can. The longer you cook it the more tender it'll be. Brisket is a tough tough cut of meat and if you don't cook it long enough it's going to be tough. It might be done and it might even have the smokeyness but it's going to be like eating shoe leather.
My dad cooks his briskets for a minimum of 6 hours most of the time overnight and it works.
6) Know the trademark signs of a good brisket. There should be a nice bright pink ring around the meat when you cut into it. That's the smoke ring...good eats if you have that. When you cut a piece make sure when you pull it it's just firm enough that it doesn't fall apart but if the little cells don't seperate under gentle pressure it's hasn't cooked long enough.
7) Are you cutting it right? When cutting brisket never ever EVER cut with the grain. It'll be tough as hell. Cut it against the grain.
8) If all else fails and you have it smoked and it's STILL tough...never fear...cook it in the oven on a very low heat. Like 300 degrees IIRC. Just wrap it up in foil pop it in the oven for a few hours and it should get a bit more tender. Not as tender as if you left it on the pit but better than chewing a piece of rawhide.
Hope that helps some. Good luck being a Texan I don't know what I'd do without brisket at least 8-10 times a year.
Oh and I almost forgot...make sure you have a quality rub to work with. Layers of flavor is what we are looking for.