Combine the light brown sugar, paprika, kosher salt, black pepper, chili powder, garlic powder, onion powder, dry mustard, and cayenne pepper in a medium bowl. Break up any sugar lumps and whisk until the mixture looks uniform, 1–2 minutes.
Pat pork dry with paper towels. Sprinkle on 1–1.5 tbsp rub per pound of meat, then massage to coat all sides evenly, concentrating on thicker sections and into crevices.
Let the seasoned pork rest 30–60 minutes at room temperature, or cover and refrigerate 4–24 hours; the surface should look slightly moistened as the sugar draws out a little juice.
Cook by smoking, roasting, or grilling as desired until your cut is done (e.g., ribs are tender and meat pulls from the bones; shoulder shreds easily). Brush off excess charred rub only after cooking if needed.
Store leftover rub in an airtight container in a cool, dark place up to 6 months. Stir before each use if it settles or clumps.