Here's something that you need to consider (or be aware of) before going to India. I've just been back from New Delhi and Agra and this is exactly what I prepared and packed for the trip. I hope this will help you.
Applying for an India tourist visa is tricky. Check if you are eligible to apply for an e-visa or not. If not, you will have to apply for one in person. You will need your travel details ready when you start your application. Basically, just do it a month or two in advance so that you get your visa in time.
Currency exchange/ cash
Indian Rupee is a closed currency so you might not be able to find it elsewhere expect in India. So make sure you take enough cash with you so that you could exchange some money when you arrive.
International bank card
It's always a good idea to have your bank card ready. Do remember to tell your bank that you will be aboard soon otherwise they might block your card for some reasons. When you see an international bank, try to withdraw some money first as not all of the ATM machine works with international bank card.
Make sure if your vaccination is up-to-date. Hepatitis A and Typhoid are usually recommended for travellers going to India. The thing is, these vaccination do not 100% keep bacteria away and good personal hygiene is a definite.
This is not particularly for India but something that you should consider purchasing. There's a lot of insurance company out there; I am sure you will be able to find one that fulfil and cover your needs!
Pack all your travel essentials like your passport, an universal adaptor and charger for your phone and camera. Keep your phone and camera with you so that you won't miss any moments.
To keep bacteria away, take some alcohol hand gel or wipe with you. Always clean your hands before eating. You will always need to take lots of tissue with you because most of the public toilets in India do not provide toilet paper rolls. Take some plasters with you just in case. Last but not least, don't forget to take a mask as the pollution is extremely serious in India, especially in New Delhi.
If you are going to India in summertime, mosquitos and bugs could be a big issue. Take an anti-bugs and mosquitos spray with you at all time to keep you away from the some disease. Sunscreen, umbrella and sunglasses are also very important too. You might also find a fan essential as well.
Ask me if you have more questions!