I go to Restaurant Depot and generally pick out the biggest ones I can find. Out here in eastern North Carolina we don't get much beef, so outside of a rare find at Walmart I'm not finding brisket very often. Sam's and Costco do small flats, probably around 4-5 Lbs, but they are fucking expensive compared to what I get at Restaurant Depot. Usually I do full packers because I like to do burnt ends with the point muscle and then slice the flat muscle. When you're picking out briskets get one that is floppy inside the cryovac. If you pick it up and it's stiff as a board put it right back down as that's going to be difficult to tenderize. If it's nice and floppy you're already in a good starting spot as that meat is pliable. As for tips go super simple... if you want to inject as an insurance policy for moisture go right ahead. A simple beef stock (or beef bullion) will do just fine and taste it... as long as it tastes good to you then it will be fine for an injection. Lots of people have methods of injecting with the grain of the meat but I go with and against so that I break all the different layers of the meat. It seems to work out well doing it this way. Ok, foil... I learned how to cook briskets going hot and fast and using foil after about 2 hours. Now I almost never foil unless I'm at a competition where they don't want a black bark, but instead a nice red / mahogany bark. So I wrap simply to keep the color where I want it and still allow it to cook. Foiling will speed up the cooking process but you will lose that crunchy bark. Easiest way to do a brisket is a quick injection, rub it down, and put it on the smoker while the meat is cold. Scientifically the meat's going to absorb more smoke when it's cold, so I have no idea why people leave it on the counter for 2 hours to warm up... seems silly and counter productive. If I'm going hot and fast (325-350°) I will usually take the point to about 207-208 internal temp and the flat to about 203-205. If I'm cooking at ~275° then I will start checking the flat for tenderness at 195° and it's usually perfect between 195-200°. Tenderness is the deciding factor and not temp. Temp is a good gauge but tenderness is what matters. I use the toothpick test where I insert a toothpick into the middle of the point (where the best slices will be) and if it's really tough and hard to insert the toothpick it's still not tender. You're looking for that toothpick to enter the meat and feel the same resistance and it would going into a jar of peanut butter. Good luck and feel free to ask any follow up questions.