We went on the 12th January in their Winter.
Here is a random list of everything I can think of:
I thought this was a great time to go as I would rather be cold and put on a jumper than be too hot. Weather in January, warm/hot in the daytime but recommend several jumpers for Taj Mahal and Varanasi and game drives which take place early morning and late afternoon. Also take a hat that stays on very well for the game drive.
The most important thing to take is ear plugs.
Although the tour guide is knowledgeable about India you can't expect him to understand the British idea of shopping as "lets find a bargain"! Our guide took us to traditional cottage industries like marble and silk. If you really want to find bargains then you will need to go off on your own. The cottage industries were interesting though if you have the patience, and at least I know what to look out for in charity shops now as I couldn't afford some of the products on offer. If you aren't interested in expensive shopping then just say so but you need to be quite decisive. Every area is famous for a special product like Jaipur is famous for gems so if you don't go the next day will be a different product.
Train is okay but take snacks like peanuts with you, our train was 6 hours late to delhi because of the fog. Take a lock and chain or even two with you for the train. A suitcase is better than a holdall as it fits under the beds in the train better.
Toilets seemed fine everywhere as Sunil was always quite fussy about where we stopped, so don't worry about them, tipping is required of course. I didn't get ill but I think I might have put on weight with all the rich curries!
I was really disappointed we couldn't go on the Elephants up to Jaipur fort but Sunil was sure the Elephants weren't well cared for so we avoided it.
If you are over 35 then you will need to do some exercies as there really is NO exercise on this trip.
Learn how to turn the flash off on your camera before Ranthambore game drive! Everyone seemed to have a problem with this! If you want to see tigers (and we saw 2, one on each game drive) then don't stop for the spotted deer, there are millions of them! The time in the park is seriously restricted and the driver will get a heavy fine if he exceeds it.
We were advised not to tip the beggars or children or mothers as it only makes the problem worse. This was one thing I was worried about before going to India and I did see some unpleasant sights but not nearly as many as I feared.
tipping is an way of life in India. Service and tax is not included on the restaurant bill and even though a price is agreed for tuk-tuks and taxis you always have to pay a tip.
With the free time in Varanasi go to Sarnath is is truely amazing.
What other people said about this trip is just about spot on, we got to see some of the best sights in the world for only 6 days off work. Every single day is an early morning though so if you suffer from insomnia or jet lag then it will be hard work.
The tour doesn't go to a Hindu temple so if you are interested then you will have to tell the guide so he can arrange something or go on your own.