This is more Tex-Mex than legitimate Mexican, but I do it all the time...
First, Chili Powder (makes about 1/2 cup) ...
3 medium ancho chiles, stemmed, seeded, torn to bits
3 cascabel chiles, stemmed, seeded, crumbled
3 dried arbol chiles, stemmed, seeded, crumbled
2 tablespoons whole cumin seeds
2 tablespoons garlic powder
1 tablespoon dried oregano (pref. Mexican)
1 teaspoon smoked paprika
In a pan over medium-high heat, toast the chiles and cumin seed, shaking pan frequently, until cumin begins to toast (4-5 minutes).
Allow to cool. Combine everything in a blender and process until you have a powder. Wait a few minutes before opening blender, scrape down the sides if necessary and blend more. Store in an airtight glass container (it will stain plastic).
Second, the Taco Seasoning (also works for soups and stuff) ...
2 Tbsp chili powder
1 ½ Tbsp corn starch
½ Tbsp smoked paprika
2 tsp ground cumin
1 tsp dried oregano
½ tsp ground coriander
½ tsp cayenne (more or less to taste)
Combine all ingredients.
Third, make Tacos!!!
½ medium onion, finely chopped
1 jalepeno, seeded and finely chopped (optional)
1 clove garlic, minced (or ¼ tsp garlic powder)
1 pound ground beef
1 recipe Taco seasoning (about 4 Tbsp)
¾ cup chicken stock (or water)
Saute the onion and jalapeno until softened. Add the garlic. Add the beef and cook until browned. Drain excess fat. Add Taco seasoning and stir to combine. Add chicken stock, bring to a simmer, and reduce to desired thickness (about 5 minutes). Salt to taste.
Serve on tortillas or taco shells with fixings of your choice.
Edit: Also works with chicken or black beans. Use 1.5 pounds sliced and cooked chicken breast or 2 cans drained and rinsed black beans. Add the chicken or beans just before adding the Taco seasoning.