No one ever goes to India and comes back un-moved - anyone who says a trip to India "was OK" is lying. That is not to say India is always wonderful, but it is always totally in your face, completely fascinating and totally and utterly different from anywhere else you have been.
I left India knowing that if I didn't leave I would have a complete screaming fit at the next person who asked me my name, I also left knowing that I would have to return - the place is just indescribable.
Pre-departure
As for any overseas travel have a medical/dental/optical check-up to avoid nasty surprises on the road. Have any recommended shots for India: a minimum is usually a booster to Tetanus and TB and a hepatitis shot if you don't have a current one. Check with a specialist in travel medicine. Bring your glasses /contact lens prescription with you and pick up a spare made in India for the fraction of the cost at home.
Check that your passport is valid for at least 6 months after your arrival date in India and that you have enough spare pages for visa stamps. Arrange your Indian visa and take out adequate travel insurance.
Bring as little as possible - ideally a carry on bag should be sufficient unless you are planning a serious trek to the Himalayas or many stays in up market hotels where you will be expected to dress for dinner. You can buy almost anything in India, tampons being a possible exception outside the cities.
On Arrival
India's time zone is GMT/UTC +5.5 so flying from almost anywhere in the world you will probably be jet lagged. Try to get onto India's time zone as soon as you leave home, try to eat and sleep on Indian time. Its easier if your flight arrives late in the day as you will probably want to sleep anyway. If you arrive early in the day try to stay awake and get out in the daylight - it helps the body's internal clock to reset. Have a short nap if you must but try to stay awake until about 8pm before crashing.
Get the equivalent of $100 in rupees cash before leaving the airport. Taxis don't take US$! You cannot legally import or export Indian currency.
Book a hotel for the first night. Use an international consolidator such as Hotel Club who offer good deals. Even on a low budget give yourself a nice hotel for the first night, 2 nights if arriving late, it allows you to ease into India. Take a pre-paid Taxi from the airport. Again there are cheaper ways to do it - but this stops the arguments about prices and meters.
Chill out - don't try to sight see and shop on your first day - relax wander around - try to get your head around India - practice crossing the road (see the video first!).
When in India
Accept that you are going to be the centre of attention where ever you go - you may think you are an olive-skinned brunette - but in India you will be immediately recognised as white. You can however make it easier on yourself by dressing conservatively or dressing like a local.
Remember that he concept of personal space is a western one and doesn't apply in a crowded country like India. You will be stared at and spoken to, they are curious not intrusive.
You will rarely see members of the opposite sex touch or hold hands in India, in contrast you will often see young men or women holding hands with the same sex. Kissing and being obviously affectionate in public is considered rude.
Cover your head (sometimes) and remove your shoes (always) before entering a temple or other religious building - this includes Christian churches.
If the touts get too much hire one, then the others will leave you alone. If you get a good one rickshaw wallah or guide doing this its probably a good idea to hang onto him for the rest of your stay in that town - you can be sure that he will suggest it!
Travel within India
The main international airports in India are: Mumbai (Bombay), Delhi, Kolkata (Calcutta) and Chennai (Madras).
Although Indian Airlines are the main internal carrier, India now has an open-skies policy which has led to many new cut-price airlines starting up and in some cases folding, stick with the better known ones.
India was built on the railway. Its is still the main form of long-distance transport in the country. There are numerous classes and trains varying from historic steam trains, quaint wooden narrow-gauge hill trains to sleek, ultra modern expresses. Basically the slower the train the less you pay - but all of them are great value. The system, though often described as a study in bureaucracy, is surprisingly efficient and now features E-tickets when booked over the Internet. Trains often have tourist and VIP quotas so you may often get on a "full" train when a local will not. A trip to India is not complete without a train ride.
There is also an extensive bus network with again buses ranging from super-deluxe to ordinary (very). One of the problems with the super-deluxe buses is the super cold air conditioning (bring a jacket) and the obligatory Hindi dance movie (at least you don't need the language to follow the plot, you've seen it before, as in Romeo and Juliet).
Keeping Safe
Despite the warnings of foreign governments regarding safety, India is a very safe destination. There are terrorists and bombings and disputed areas but these tend to occur near the Pakistani, Chinese and Bhutanese borders, areas where you won't often be allowed to go as a tourist anyway.
Petty theft is common and the pickpockets are very,very good. Do not carry large amounts of cash in your wallet or a back pocket. Do carry enough for a day or so expenses in a wallet in a front pocket and keep most of your wealth hidden. Be aware of who is watching when getting money from ATM's. Theft at knife or gun point is lot less likely than in countries such as the US or UK.
Although women may get stares, rude suggestions and the odd grope, you will be unlikely to be seriously threatened. If you get uncomfortable appeal for help from couples or women - the haughty "you talking to me" attitude is usually effective.
In cheaper hotels check that your windows and doors are secure before you take the room - you make want to bring your own padlock for added security.
The most dangerous thing you will probably do is take a bus or cross the road - watch the video if you don't believe me!