The main heat source in my pit is from the bottom, and I cook my brisket fat cap down as a bit of a shield from the heat source, so I leave about 1/4" of fat on that side of the brisket. Otherwise I trim the hard fat and most of the fat between the plat and the point to make it easier to separate them later. On the other side of the brisket I do trim off as much as i can so i have more meat for the rub to adhere to.
Is all of this right? I don't know. Are there other ways to do it? Yep! But this has worked well for me.