Be safe
Always keep your passport and any other important papers close to you. Don't leave important documents in your luggage. Also, keep two photographs and your passport information in a safe, separate place in case your passport is lost or stolen.
Contact the state ITDC (Indian Tourism Development Corporation) or the state tourism office (usually located in the capital city) for travel information. The ITDC location information can be found in a local phone book.
Keep your money in several different places. Act like you knows what you're doing and where you're going at all times. Dress in traditional clothing whenever you travel and avoid travelling alone in the night.
Stay healthy and avoid street food.
Always carry a water bottle with you. Don't drink the local water. Either boil your own water or make sure to buy bottled water from a reliable distributor. Indian drinking water contains many forms of bacteria that cannot be filtered out by using a simple filter. Only eat fruit and veg with skins (e.g. bananas). Indian street food is spicy and tasty but unhealthy. So if you eat on the street, consume only food that is fried or boiled. Food that hasn't been cooked at high temperatures could make you sick.
Equip yourself with preventive medicines and basic first aid equipment before you leave home. Having these supplies will save you the trouble of going in search of a doctor or drugstore if you get sick.
Be prepared for noise and avoid the crowds
One way of ensuring you can have a bit of personal space, albeit in your head, is to have earphones with you to shut out some of the surrounding – there's nothing like the sheer clamour of an Indian city. Always try to avoid the crowds.
Make your travel plan according to your interests
Think about what interests you, what you like doing, and tailor your trip accordingly. Here are some places in India according to interest -
Shopping - Delhi, Bangalore, Mumbai
Beaches - Goa
Trekking - Himachal Pradesh, Uttrakhand, Kashmir
Yoga - Rishikesh, Haridwar
Thrill-seekers - Manali, Leh, North-East city in India
Religious fervour - Varanasi, Vrindavan, Haridwar
Fort and Culture - Rajasthan
Avoid deals that seem too good to be true
Government shops are probably the easiest way to avoid running foul of scams, but simple rules like paying for things with cash, to avoid card cloning scams, may save you a lot of unnecessary trouble later in your journey. You should also pay particular attention if you're arranging to have things sent home by post, as it's not unknown for shops to take your payment and send worthless items instead.
Indian people are so friendly
Indian people are so friendly and always ready for help. You absolutely can try to talk to them on trains and buses and most times they will be happy to do so- they'll even let you take photos of them. They might stare sometimes, but it’s just curiosity and isn't as rude in their culture.