For street tacos, I prefer corn tortillas over flour, but they need to be homemade or from a good store. Crap like Mission taste like cardboard. I use flap meat trimmed super thin. A simple marinade with 3 cloves garlic, juice from 2 limes, 1/4 cup Worcestershire, 1 tbsp brown sugar, 1 tsp salt and pepper. Marinate just for a couple of hours. Grill the meat, chop it up and finish it up on a griddle while cooking the tortillas. Serve with chopped onion, cilantro and a raw avocado tomatillo salsa.
For the salsa,
Put 1/2 pound of tomatillos, 1 avocado, 2 or 3 serrano, a 1/4 white onion, a handful of cilantro, 1 tsp salt and about a 1/2 cup of water in a blender