Lightly crush the celery seed in a mortar and pestle or under a rolling pin until fragrant but not powdered.
In a medium bowl, whisk together sweet paprika, light brown sugar, kosher salt, black pepper, garlic powder, onion powder, dry mustard, and cayenne pepper until uniform; whisk in the crushed seeds.
Use immediately by patting meat dry and applying 1–1.5 tbsp rub per pound, pressing to adhere; let seasoned meat rest 20–30 minutes before cooking.
Store leftover rub in an airtight container in a cool, dark place up to 3 months; stir before each use.