Coat with olive oil, salt, and pepper (some kind of rub if you want also but it's not necessary).
Fat side up in a pan with 2" sides. You want part of the meat to be above the top of the pan. Last time I cooked mine on 225 but 250 will be fine. Depending on the poundage, time will vary. You want the internal temp to reach 200 degrees. I know pork is done sooner but the whole purpose of cooking a Boston butt is to have it pullable. DO NOT COVER while cooking. This will give the whole outside a nice crust and keep the inside moist and tender.
I cooked one (can't remember poundage but it WAS a big boy!) and it took almost 20 hours. Another one took about 8. The key though, like I said, is getting it to an internal temp of 200. And those browned harder bits on the outside of the meat are "prime" good eats. Don't throw those away, devour them when no one is looking!
Once at 200 let rest for about 20 - 30 minutes before slicing. If you slice too soon you will lose all the juice that keeps it tender. Remove fat cap and start pulling the meat in shreds. You can also keep in chunks if you'd rather eat it that way. Either way it's going to melt in your mouth.