Yellow fever certificates must be shown by travellers arriving from Africa, Latin, America and Papua New Guinea. Other shots, although not officially required, are advisable. Typhoid, Polio and tetanus are important. A gamma globulin injection for hepatitis immediately before departure is also advisable. Many countries require arrivals from India to have an up-to-date cholera vaccination. 
A Vaccination against rabies is now available but you must still visit the nearest hospital immediately following any bite from a dog or monkey for a further course of injections.
Malaria is still widespread in many part of India. Advice as to which pills to take is constantly being revised but at present one suggested regime is Niva-quine (or Avloclor) twice a week and one or two paludrine daily. both courses must be continued for four to six weeks after leaving an affected area.
Most modern medicines are available over the counter in India but it is wise to have your own small reserve stock. If prescription drugs are required bring enough for the duration of your visit. It is advisable, to keep a second stock of these packed in a separate bag in case you lose your baggage.A small kit should include a remedy for 'Delhi-belly' (upset stomach), some antiseptic cream, lip salve, mosquito cream, suntan lotion for log days on Goa' s beaches, water purifying tablets if bottled water is not available, elastoplasts, etc. 
Many tourists develop problems on their second or third day because of 'climate shock' (heat exhaustion rather than contaminated food and water), ut if a upset stomach persists seek medical advise (big hotels have a doctor o call). Many people in India advise drinking lots of fluids (boiled and filtered water with a little salt ad sugar) and keeping to a diet of rice and yoghurt for a couple of days
There are a few things to be careful about in India health-wise. Drink plenty of fluids but never drink tap water. the flask in hotel rooms contains filtered water and bottled water is now available almost every where. Avoid fresh salads even in hotel, and do not eat street food until you know how much you can abuse your body for the sake of your palate.