Loose cottons are your best bet in the Indian summer. Travel light as laundry services are commonly available at very nominal prices. Remember to use sunscreen and wear sunglasses.
Children (and sometimes adults) tend to be intrusive in rural areas. They usually mean no harm. It is advisable to ignore such intrusion. Discourage begging as much as possible.
It is advisable to drink only bottled water. Insist on sealed bottles at hotels and restaurants.
Beef is not served in many parts of India. Pork is also not easily available. Try traditional vegetarian cuisine too - the sheer variety will not fail to impress you.
Food can often be spicy. Order a side dish of curd or yogurt to balance the spice.
Drink lots of water and fluids to counter the dry heat. Coconut water is an excellent tropical option.
Try to shop in government handicraft shops & few other private shops where the prices are fixed and the quality is certified. Bargaining is a standard practice in most other places and is entertained by all. If possible, take someone who is familiar with the area along when you go shopping. This can help you avoid being overcharged.
In hotels and restaurants, tips are not normally included in the bill. You are free to decide a standard tip (usually 10%) depending on the service. Some hotels include service charges on their bills. In such cases tipping is not necessary.
In hotels, porters, taxi drivers and room service attendants are normally tipped at the end of the stay.
Dress codes for religious places can include covering your head, being barefoot and being modestly dressed. Ask, so that you don't unwittingly give offense. Some temples do not permit any leather articles at all on their premises.
Most museums in India are closed on Mondays and Site Museums, those near archaeological monuments, on Fridays. Photography is not always permissible, and at many places it is permitted only at a fee. There is usually a higher fee for using a video camera.
Smoking is not allowed at public places. All properties of the Indian Railways including trains and railway stations are strictly non smoking zones with stiff penalties on violations.
English is spoken at almost all tourist centres, but you can also request Government-trained and approved guides who speak different languages like German, French, Spanish, Japanese, Italian or Russian.
Always carry a kit of the basic emergency medicines you might need along with mosquito repellent.
Always give yourself extra time for whatever you may have to do. Make allowances for delays here and there. Keep extra photocopies of the relevant pages of your passport. This will be required for Indian permits. Also, keep a few extra passport size photographs.
Insist on the taxi/auto meter being flagged down in your presence. As much as possible, especially from the airport or railway station, insist on using the pre-paid services which are available at most important places.
In cities you can change major foreign currencies and any brands of travellers' cheques - but you'll widen your options and save yourself hassle if you stick to US dollars or pounds sterling, and either Thomas Cook or American Express travellers' cheques. Most big cities have ATMs which accept Visa, MasterCard and American Express. The ATM network is ever expanding and in some states, you can find them even in some smaller towns.