Add all ingredients for dry rub to a bowl and mix well until combined. (Or use your favorite pork rub.)
Rinse meat and pat dry with a paper towel.
Sprinkle dry rub on all sides of the meat and rub into the meat until well-coated. You don't have to use all of the rub, but enough to liberally coat all sides of the meat.
Wrap meat in plastic wrap and store in the refrigerator overnight. This really helps the flavor!
When ready to cook, place pork shoulder in the slow cooker and add several shakes of worcestershire around the bottom but not directly on the meat so it doesn't cause the rub to come off.
Cook on low for 8-12 hours. Less for smaller pork butt and more for larger. You''ll know it's done when it's falling apart and very tender.
Shred the meat in the slow cooker, taking care to get some of the juicy renderings mixed in.
Serve plain or over rice, or with barbecue sauce for sandwiches.