Bake the pork. Heat the oven to 325 degrees. Lay the pork on a cutting board and sprinkle all sides liberally with salt (you’ll need at least 2 teaspoons). Nestle the meat into a baking dish just big enough to hold it (it usually fits in a baking dish about 7x11 inches) and drizzle the water or orange juice on and around it, lifting to allow liquid to run under the meat. If using the optional flavorings, nestle the garlic and bay leaves around the meat (both should be in moist places), then sprinkle with oregano and black pepper. Cover tightly with foil and slide into the hot oven. Set the timer for 1 1/2 hours.
Brown the pork. Remove the pan from the oven and uncover. Test the pork: it should be almost tender when pierced with a fork. (If the meat is still very firm, re-cover and bake for an additional 20 minutes or so, then re-test.) Raise the oven temperature to 450 degrees. Slide the uncovered pan back in the oven and roast until all the liquid has evaporated and only the rendered fat remains, about 30 minutes. Use a large metal spatula to turn the meat over, break it into large chunks, return to the hot oven and roast for another 20 minutes or so, turning the meat every 7 or 8 minutes, until the carnitas are richly golden all over.
Serve. Arrange the carnitas on a warm serving platter and sprinkle with salt (a good finishing salt is welcome here—I’m particularly fond of Maldon). Serve with the guacamole, salsa, limes and warm tortillas. Encourage your guests to pull apart the golden pieces of deliciousness, fitting several pieces on each tortilla, before topping with guacamole, salsa and lime.
Working ahead: Once the carnitas have been browned, you need to serve them right away. You can, however, braise the pork up to a couple of days ahead, cover and refrigerate it. On the day you’re serving, let the pork come to room temperature, and, an hour before serving, roast it.