...pick a brisket.
If I say brisket what do you picture? Hopefully at least a delicious piece of meat. The confusing part for most folks that are just getting started and a few that have been at this a while is that there are three cuts that are referred to as brisket; whole, flat, and point. The whole brisket is the entire primal cut just as it comes from a meat packer and is typically found in a vacuum sealed package. The flat can also be found packaged that way, but it will lack the noticeable bump on one end that is the point. I suppose one could buy just the point, but I have never seen one that way. Since there are flats by themselves the points would have to go somewhere-- probably some really tasty ground beef.
While I prefer cooking a whole brisket I will gladly cook a flat. The flat typically will have less fat on it and you should always look for one that is in the cryo-pac as opposed to one a butcher has totally trimmed down. If you feel that an entire flat is still more than you want to cook it is possible to cook a 3 to 5 pound flat that has been trimmed. This is where a few slices of bacon and a foil pan will come in handy. More on that later.
So lets talk whole brisket. A good butcher is your friend in this search and really in any barbecue endeavor. Find a good one and make friends. When it comes to picking a brisket some will tell you that a Wagyu or Prime cut is required to make the best brisket. I certainly respect their credentials and for their purposes that could indeed be true. For my purposes it isn't. A regular choice brisket will do nicely and will have more than enough marbling to get us to tasty and unctuous barbecue. When you get to the butcher or market hopefully they will have more than one for you to choose from. Pick it up. Does one bend more than the other? Flexibility is a good sign of future tenderness. Does that fat look nice and white on both? It should. There will be some brown and yellow pieces we will trim later, but by and large the fat layer should be snow white and look appealing. Flip it over. Look for silver skin. This will need to be trimmed off and you are paying for it so all things being equal by one with less of this. Poke around gently. Feel for the hard fat. There will be some, but again, there isn't any sense in paying for a larger brisket that will just need trimming later. I also like to look for as large of a point as I can find. So if everything else looks about the same I will take the brisket with the larger point. Just my preference. Truthfully if you have a reliable source and the beef looks fresh most any they give you will do.
Once you have it home leave it in the cryo-pac until you are ready to rub. Just put on the bottom shelf in the back of the fridge and it will be just fine for a few days and maybe longer. A few more things are needed and the next step is the rub.