There are a few things you need to take care of, before travelling to India:

Visa
There are three kind of visas for tourists. The 15-day single/double-entry transit visa. This visa is valid for 30 days from the date of its issue. The 3-month multiple-entry visa. The visa is valid for 90 days from the date of first entry into India, which must be within 30 days from the date of its issue. The 6-month multiple-entry visa. This visa is valid for 180 days from the date of its issue, not from the entry into India.

Visa Extension
It is virtually impossible to get the 15-day or 3-month visa extended. Only the 6-month tourist visa can be extended. It can be quite a bother to extend it beyond a 15-day period. Avoid it unless there is an emergency.

A 15-day extension on the 6-month visa is issued by the Foreigner's Regional Registration office (FRRO) at any of the four metros: Delhi, Calcutta, Mumbai and Chennai. The FRRO office is open on weekdays, 9.30 am to 1.30 pm and 2 pm to 4 pm. A 15-day extension is given only if confirmed air tickets are not available. No fee is charged.

New Delhi : FRRO, Hans Bhawan, I Floor
Bahadur Shah Zafar Marg,
Ph : 23319781

Calcutta : FRRO
237, AJC Bose Road,
Ph : 2473300

Chennai : FRRO, Shastri Bhawan,
Haddows Road, Nungambakkam,
Ph : 8275424

Mumbai : FRRO, Dr. D. N. Road,
(Near Police Commissioner's office),
Ph : 2620446

Travel Insurance
Take a travel insurance policy, covering theft and loss, before coming of India. Also buy a medical insurance. There are several kinds of insurance policies. Make the right choice after consulting a reliable travel agent in your country.

Driving License
A valid International Driving License (IDL) is necessary if you wish to drive a car or a motorcycle in India and it is advisable to get one before coming. If you do not have an IDL and still wish to drive in India, you can get a Temporary Driving License, provided you are carrying a valid driving license of your country. You may still be required to take a test to check your knowledge of road signs.

Tax Clearance Certificate
If you stay in India for more than 120 days (4 Months) from the date of issue of visa, regardless of your date of entry into India, you would be required to furnish a tax clearance certificate to leave the country. This is to prove that you did not earn money while in India and that your trip was financed with the money brought in. If you are planning to stay in India for more than four months, be careful with your documents relating to travel.

If you are not an Indian passport holder and you are planning to stay in India for more than four months , apply for the certificate at the Income Tax Department, Central Revenue Building (ITO), Vikas Marg, New Delhi (Ph : 23316161, 23317828).

Foreign Travel Tax
A person will have to pay Rs. 500 at the airport as Foreign Travel Tax when leaving the country. For travel to Pakistan , Nepal, Sri Lanka, Bhutan, Myanmar, the Maldives and Afghanistan, the tax is Rs. 150.

Customs
There are two channels for customs clearance at International terminals in Indian airports: Green Channel and Red channel.

(1) Green Channel: This is for unhindered exit from the airport. you can walk through the green Channel if you are not carrying goods which attract customs duty.
(2) Red Channel: For those who have anything to declare, including money worth more than US$ 2,500.