Combine paprika, cumin, pepper, and (if desired) crushed red pepper and cayenne in a clean glass jar with a tight-fitting lid. Secure the lid and shake until the seasonings are mixed well. Store in the refrigerator for up to 6 months.
To make ahead: Store in an airtight container in the refrigerator for up to 6 months.
Associated Recipes: Spice-Roasted Chicken & Lemon Potatoes