Welcome to India! It is dirty, loud and overwhelming. But you'll get used to it.
But before you even get on the plane, you should know these things...
Unless you are going somewhere where malaria is definitely present, don't take the freaking pills. You probs aren't going to even come close to getting malaria but I can guarantee that one day you will forget to take your pill until just before you fall asleep, you'll take it, and then you'll feel like there is vomit rising in your throat for the next 3-5 days.
Know that you will get a stomach thing. If it's your first time, it's inevitable. Be as careful as you feel you should but it really doesn't matter. You will get sick. Probably just for a day or two (if you're unlucky though, ummm...) and then you'll be fine. In fact you'll be better than fine because, having already spent a few days becoming intimate with the hotel bathroom- and hopefully, for your sake, it is equipped with a western toilet- you will no longer be afraid to eat street food; the worst has already happened...what's left to fear? And street food is sooooo cheap and sooooo good- usually. Occasionally there is a deep fried thing that looks fantastic and tastes of old oil.
If you are caucasian, but especially if you are caucasian with blonde hair, and especially especially if you also have blue eyes, be prepared to be in a lot of very awkward group pictures with Indians you have never spoken to. You may have to hold a random baby and smile in a family pic, you will definitely be one of the star attractions at any destination which is popular with domestic tourists and I would really recommend avoiding anything that even has a whiff of bikini about it at the beach.
OK. They are some of the things I would probably have liked to know the first time I stepped off the plane onto the subcontinent. Now for everything else...
WHAT TO PACK
A lot of loose, comfortable clothes that are also stylish. And if you don't have any at home, then wait til you get there and buy some. Because Indians dress up when they go out, even if it's just down to the supermarket. And they will judge you if you look like a smelly backpacker who hasn't washed for days- because Indian people are also very clean.
Savoury crackers. You know, Vita Wheats, Sayos, those weird yellow cheese ones... In all my time in India I managed to find one brand- ONE BRAND!- of savoury crackers. And this, in the land of the biscuit. Truly, the Indian people love a biscuit- a SWEET biscuit. There must be a million and one varieties. But a suitable vessel for a vegemite snack? There were a lot of crackers that advertised "salty' but which tasted like a sugar biscuit with some salt mixed in. So you'll be wanting some home-grown crackery goodness.
NOT guidebooks. Indians are smart, and unless the guidebook was only published half an hour ago, they will have figured out the recommendations and put the prices up/started a copycat business in the same general area. And when I say copycat, it will be exactly the same as the original- name, colour, product- except more crap. Also everybody has a guidebook, you'll just be trailing the hordes. So just take some good maps (so when you get off a train you have some actual proof of how far away you are from where you want to be...rickshaw drivers are not your friends), some advice from friends and a laid-back attitude. And if you really, really, need some travel advice? Everybody you meet- foreigner and Indian- will be more than happy to pass on what they've discovered/think you MUST see.
A sense of humour and a fatalistic attitude. It will serve you very well indeed.
JUST SO YOU KNOW
Never, never, never, never get angry. Or if you do, be prepared to be completely ignored from that moment on. Getting stuff done is insanely tricky in India (unless you can figure out when you are required to slip a few rupees under the table...I was never good at that though) and it is very easy- I would say reasonable, even- to get angry, start screaming and shouting and pulling out chunks of your own hair in a crazed fit of frustration. But it will. not. work. You will become invisible immediately, your problem relegated to that place on Earth where things never to be solved live on in confusion for eternity. I have seen this happen before my very eyes (and let me tell you, it does nothing to ease the anger) and if we were sitting together over a cup of tea and a slice of cake I could tell you some hilariously ridiculous stories about Indian bureaucracy. But we aren't. So just remember this: "everything is fine, no problem, really, just one small problem...", remember to keep smiling and remember that some problems just weren't meant to be solved.
Be prepared. Be prepared to be tricked by India. Because once you have been there no place on Earth will be as bewildering, crazy, hysterical, infuriating, shocking or beautiful. You will always be drawn back. I really hated India the first time I went and vowed never to return to its wretched shores. But inevitably I did, and now I always will.
It's a confounding place. In the most fantastic way.
And the food is incredible.