If you're making these beef tacos for a large crowd, there are several ways you can keep them warm. I like to place them in a baking dish and bake them at 400°F for about 10 minutes. Then turn on the "keep warm" setting and let them sit in the oven until serving. This will ensure they stay warm, but don't overcook and get too crispy. You can also cover them tightly with aluminum foil to help keep them warm as well.