A lot of good suggestions have been made and should be noted. Permit me to offer some suggestions:
You might trim the large "chunks" of fat from the brisket but is not necessary. This fat just won't render.
Allow the brisket to reach room temperature, it will cook more evenly. Season with a generous amount of salt and pepper. You may add other spices if you choose but it is not necessary and some may actually alter the real flavor of the meat. If you want onion, have onion slices on the side.
Cook brisket s l o w l y using indirect heat (do not cook over the fire, it will be tough). Use a good hardwood, hickory is fine, no aromatic woods. Cook S L O W L Y to an internal temperature of about 145-150. At this point the meat will have a nice "bark" on it and the "pink to red smoke ring" will have formed.
The meat will not absorb any more smoke. Wrap meat in the pink or white butcher paper, do not use freezer paper and continue to cook S-L-O-W-L-Y until the meat reaches an internal temp of 200-205 degrees. Remove meat from pit, place in large pan and cover with several layer of old bath towels. Let the meat rest for a couple of hours. Cut meat ACROSS the grain in quarter inch slices (not sure what that is in metric) and serve with pickle, onion slices, and plenty of good bread. Dill is my pickle of choice. I have placed as high as first in brisket BBQing competitions using this basic method.
Because real brisket cooks take their cooking seriously, I know there may be some criticism and I as a serious brisket cook will probably resent this but this was aimed at Geoff for a first time brisket Bar B Q cooker. I know some of you can tell the internal temp of a brisket by just looking, touching, holding, or maybe just asking it.
From a South Texas BarBeQue guy,
Riesel
Did I mention cooking the meat SLOWLY???