Hi Dave,
First a disclosure: I was born in India and moved to the US years back.
What kind of photography or sight seeing would you like to do in India? I think this is the most important question you should get answer to. I find following type of photography very interesting in India:
Architecture: the centuries old temples and forts in India have no parallels. The intricate stone structures in temples are just mind-boggling.
People, traditions and festivals: The variety of people in colorful dresses and costumes makes India quite unique. As you travel from state to state the traditions, dresses, festivals and languages change. It is an interesting experience to attend an India wedding or be at a place during a festival.
Landscape: From tropical forests to backwaters of Kerala covered with coconut trees to deserts of Rajasthan to beautiful warm beaches along the west and east cost to mountains covered in coffee/tea/spices plantations to majestic Himalayas, there is a lot to choose from. There are some coastal islands that have pristine beaches and are quite beautiful.
Wildlife: I have not seen the variety of birds anywhere else (I used to be an avid birdwatcher). Also, among other commonly seen animals (e.g. deer, bison, etc.), tigers, lions, rhinos, elephants could be seen in certain national parks and wildlife protected areas.
Many of the common precautions such a bottled water, toilet paper, vaccinations have been already mentioned. You will need to get used to a lot of people, chaotic traffic (this is an understatement no words can describe the traffic) and pollution in big cities. Do take warm clothing if you are visiting cold places. There is not much air conditioning in public places and cabs. You might also want to carry insect repellents and mosquito nets, if you are visiting remote areas with small hotels. Last year when we visited a national park, these items saved our trip. Dont forget a flashlight - the electricity is not as reliable as in western countries. Thankfully you are going in cold season, so lack of electricity wont leave you sweating in hot 100+ degree temperatures. One can be prepared for the cold but not from the heat and humidity when electricity fails. Dec. to Feb. is probably the best season to visit India.
Enjoying India is in many ways a state of mind. People love India when they are able to ignore/overcome minor inconveniences and annoyances and start enjoying what is uniquely Indian variety, food, spices, people, cultures, festivals, dresses/costumes, languages, temples, forts, beaches, backwaters, coconut trees, coffee and tree plantations, birds, Himalayas,
I was fortunate to have parents who loved to travel and hike and had financial means to do so. I have traveled extensively in India including many non-touristy places. Feel free to contact me if you need any info.
// Atul