Lots of great info in this thread!
I would add that at the end of the day you just have to do it, a while back when I was working on my brisket, I would cook one once a week to nail down the variables. I started to get consistent results at about #20 and another 20 I had my rub down pat.
Every cooker is different and while I would say that there is no bad advice in this thread there is also lots of room for finding your own way. I do not foil any of my BBQ at any point in the cooking process as an example. As my friend and mentor Tom has said many times- "Relax its just BBQ!"