Visitors are not to be expected to tip taxi drivers for short trips and tipping is not prevalent in restaurants.
However, hotel, airport and train station porters should be tipped, about 20 rupees / bag.
With respect to guides and drivers, check to see if a service charge is included with your purchase. If not, a 10% gratuity or 200 rupees per day is appropriate.
We've decided to tip 10% in restaurants, especially those where we expect to be return patrons. We give our Deloitte driver about 500 rupees a week. While the drive to and from work is very short, Kaleem has been really helpful on the weekends, when we are in town!