THE most common mistake by far is not giving it enough time, so I'd start the evening before, not the morning of.
After the meat gets up to about 194, I start checking the shoulder blade to see if it is lose and ready to pull clean. I'll also check to see how it's holding together. I want to pull it off the pit before it's completely falling apart if I can help it. Sometimes it's like that at 200 on the mark, sometimes a few degrees before.
Have fun with it! My first ribs sucked. My first butts smoked!