Besides good quality and comfortable walking shoes carry sandals. Keep a set of one-piece bathing suit along with cotton undergarments. Synthetic inner wear are fit for cold mountain region. You will face pleasant to extreme cold climate in mountains and hill station depending on seasons and height.
On using Public transport like bus/metro/train, confirm that you are entering in ladies coach otherwise you might have to face huge crowd.
When traveling in public transport, make sure you are paying by meter.
India is incredibly beautiful with its natural resources. Your video or still photography will be life time collection. Get an Indian sim for your mobile to stay connected with your group and tour planner.
In fact, you don't need to bring cloths to India because you can buy there at very low price. If you land in Delhi, go straight to any of the Fabindia outlets and stock up enough inexpensive cotton "salwar suits". The three-piece suit called Salwar Kameez in Hindi consists a long or short tunic worn over fittings or loose fitting pants and a long scarf, called 'Dupatta' to wrap over. These outfits are suitable for the climate and for maintaining decency and modesty that may help you Dress Conservatively.
Don't go by Bollywood divas with skin tight revealing dresses and dress decently even if you wear western outfits. Salwar suit with long scurf of light weight fabric would also help to get entry to Mosque, Gurdwaras and traditional Hindu Temples. Saree, a long piece of fabric is difficult to wear and carry, but salwar kameez are really comfortable for journeys.
Carry small locks and a cable lock for your bags and zippers. These are very helpful in many over night train journey. Locking your luggage to the seats or berth would ensure security from theft. Locking the zipper would be an extra protection against theft. Travel Companies like Hellotravel.com can connect you to verified travel agents and help plan the best tour for your tenure in India.
Goa is a prime spot where you can find western culture and local people are used to sea white or foreigner women with two piece swim suits. Kovalam in Kerala is also foreigners' destination.
It is simple to say, but difficult to practice. Take healthy food that matches your food habit, avoid road side junk foods though they are too tasty to ignore and drink only boiled or bottled purified water which is often referred as mineral water in India. Keep a hand disinfectant to use before eating by hands. Do exercise and try Yoga for long term benefits no matter wherever you stay or go.
You should keep your immunizations updated. But medicines are available in cities at cheap rate when you carry dollars or similar currency. Medical treatment in urban area is of world standard yet affordable for foreigners.