Buy the best meat you can find. We're lucky having a butcher nearby that supplies to competition BBQ'rs.
As they say, junk in junk out. Apply your rub the night before. Bring to room temp and stabilize your grill at 225 deg. I use a Kamato Joe. Apply your fav wood chips for the first hour or so. I use hickory. Be sure to add a pan of water in the grill and don't let it dry out. Bring internal temp to 165 deg. Then wrap in foil to help break thru the stall. Remove at 200 deg or so and then place in a cooler to let it rest. Total cook time for a 15 lb brisket is about 8 hours.