You don't flip them - Keep it fat side UP and leave it alone. Be sure to toss in a mesquite chip from time to time and for a really good flavor, toss in a little pecan and hickory with the mesquite..
Since this is your first, maintain the temp around 225-250. Cook for at least 12 hours, but I suggest to cook it about 6-8 hours on the grill (indirect heat) and then
transfer to a foil covered pan and cook at 210 for another 6-8 hours or longer if you chose. The longer you hold it at 210, the more tender it will get. Obviously a large brisket will require a little more time than a small one.
It will melt in your mouth, I guarantee it!
Good luck!