Here's how I do mine, just so you have an idea what to expect. This is by no means the right way or the only way, it's just what I prefer; After removing the brisket from packaging, i rinse it in cold water and pat dry with paper towels. Then I feel around the fat cap side for any real thick spots of fat, and trim down so the entire fat cap is around 1/4" thick. Heavy spots of fat are usually along the edges and on the point.
Then I flip it over and trim off almost all the fat from the bottom and remove that large chunk that sits between the flat and point. This is all personal preference though, trimming the bottom this way I've found gives me better smoke penetration and a better bark. Apply your favorite rub and smoke away. I smoke mine fat cap down to protect the meat as I do not wrap my brisket.
Trimmed bottom (meat side)
Trimmed fat cap side
Just an idea of the meat side pre-trim