Travel healthy. Once on the road (or in the air ), take all precautions that will keep you from that running nose (or tummy !), dizzy body temperatures, giddy hangovers etc. Make sure you don't embark on a trip even if there are some early signs of a sickness.
Cholera, dengue fever, dysentery, hepatitis, malaria, meningitis (trekking areas only) and typhoid are the risks here.
Travelers from the US, Canada or the United Kingdom do not require any vaccination certificate. Though normally, an International Health Certificate is not asked for by the immigration officials, its always better to carry one. Remember to play safe ! God forbid but just in case you need medical attention, this will be an invaluable piece of paper. Carry certificates like the one for Yellow Fever Vaccination.
If you believe in taking precautions, take all the vaccinations one needs. To avoid malaria and dengue, carry mosquito repellents, nets and sprays. If you can bear the heat, wear clothes that cover most of the body.
The best thumb rule is to be a careful about food and water. Eating raw salads and fried food from a street-side vendor is a no-no. Avoid pork too. If the temptation is soaring, go to a clean restaurant that you can trust. Eat balanced and healthy meals. Keep popping those friendly multi-vitamins.
Water has to be from a reliably clean source. If not sure where the water comes from, ask for a known brand of mineral water. Always carry a water bottle with you - this will save you from dehydration too. (Make yourself a quick salt-sugar solution - 1/2 tsp. salt and 4 tbsp. in one liter of water - to re-hydrate those parched cells). If you cannot lay hands on branded water, use chlorine / iodine tablets in water. These kill germs that can cause water-borne diseases. Read the instructions carefully and do not overdo these.
Carry a first aid kit with adhesive bandages, thermometer, water-purification tablets, antibiotics, antiseptic creams and mosquito repellents.
If you fall ill, see the doc and keep cool. Tell yourself that this too shall pass !
Sun and Heat Protection :
Southern India is HOT, especially during the months, of March, April, and May. The sun is very strong when you're so close to the equator. You can protect yourself in a variety of ways.
Some Indians, women especially, carry around umbrellas that have a silver underlining to reflect the sun's rays. Plan to buy one of these when you arrive. Sunscreen is also helpful and available in India. Some volunteers regularly use it; some rarely do. Bring at least one bottle of SPF 15 or higher.
Expect to sweat a lot. Indians deal with this by using talcum powder to absorb the sweat. Plan to purchase this when you arrive.