Here's a recipe I've used to make my own...but you can also just use a seasoning packet from the grocery store.
http://allrecipes.com/Recipe/Taco-Seasoning-I/ Ingredients
1 tablespoon chili powder
1/4 teaspoon garlic powder
1/4 teaspoon onion powder
1/4 teaspoon crushed red pepper flakes
1/4 teaspoon dried oregano
1/2 teaspoon paprika
1 1/2 teaspoons ground cumin
1 teaspoon sea salt
1 teaspoon black pepper
Directions
1. In a small bowl, mix together chili powder, garlic powder, onion powder, red pepper flakes, oregano, paprika, cumin, salt and pepper. Store in an airtight container.