Rules of thumb I keep in mind...
1. It's done when it's done. It typically takes me around 14-16 hours to finish a 9.5 lb. pork butt. Leave it in until it hits 195 as an average from the multiple spots you take its temp.
2. I try to keep the temp. in my smoker roughly between 225-250, and only worry about smoke for the first few hours.
3. Don't worry about using too much rub. Rub is good. A thin layer of yellow mustard can help it stick to your butt. Don't worry - it won't taste like mustard.
4. Your rub can be complex, or a simple as some kosher salt, paprika, brown sugar, and chili powder.
5. Let the butt rest for about an hour after it is removed, and before pulling. Wrap it tightly in foil while resting. If you want to keep it warm for an extended period of time, place the wrapped butt in a cooler, covered with a towel.
6. Serve a variety of sauces on the side, but leave the meat more or less alone. I like to serve it with a mustard based sauce, a vinegary sauce (my favorite), and a typical bbq sauce for those who enjoy that.
7. Don't panic if the pork butt's temperature stalls around 170 degrees for a few hours. It happens. Just keep the temp. in your smoker consistent and ride it out. It will start climbing again... eventually.