The best fish tacos require good fresh fish, good tortillas, and good salsa. Look for freshly made corn tortillas at a Latino grocery—they are always superior to those found in supermarkets. And homemade salsa is always better than store-bought.
Set all the accompaniments out on the table so everyone can assemble their own taco, folding a steaming hot tortilla around a chunk of grilled fish, and adding avocado, salsa, cabbage, and lime. Have a big tub of beer on ice. For dessert, cut up a watermelon, or serve paletas, frozen fruit ices on a stick sold in Mexican groceries.