In major urban centres, there are many restaurants and fast food joints that follow a homogenized "global" etiquette. However, in mainland India, there still exists a uniquely Indian etiquette. Here is more on this etiquette.
While eating at any restaurant, basic etiquette involves leaving a good tip for efficient service and being courteous to one's host. As far as Indian restaurants are concerned, many of them are not too formal. However, there is a set of basic rules that must be followed everywhere.
