Before traveling to India, it is important that you apply for an Indian E Visa. If you are not sure whether you are eligible for an E Visa for your trip, then you can get information about the visa requirements and application process via the Indian High Commission website.
You will need to make sure that the visa you apply for is the correct type for your intended trip, and that it will cover the duration of your stay and allow you to engage in the activities that you plan. If you enter India using a visa that does not cover the purpose and duration of your stay then you risk being deported, or being detained upon arrival and you could lose your right to enter India again in the future. Note that the rules for Business Visas in particular are strict and you cannot extend the duration fo a Business Visa while you are in the country.
The permitted duration of stay for a double entry tourist visa is currently 60 days, and this covers the Indian E Visa for tourist travel. There is also a double entry business visa, and a triple entry medical visa. If you are travelling through India, but not planning to stay, then this is covered by a Transit Visa. There are some rules regarding re-entering the country for people on tourist visas, but these rules are complex and there are rules that are specific to people from different countries too, so it is a good idea to seek advice before planning your trip.
If you are of Pakistani origin and hold dual nationality (e.g. Pakistani-British) then you will need to apply for the Indian Visa using the Pakistan passport. If you are of Pakistani origin and renounced that nationality or cancelled your Pakistani passport then you will be asked to provide proof of this when you apply under your current passsport. It may take eight weeks or more to process such an application, so you should make sure that you apply well before you are planning to depart for your trip.
All applicants are required to have a machine readable passport with at least two blank pages in it, which has a remaining validity period of at least 180 days at the time of application. Ideally, you should have at least 180 days of validity remaining upon arrival in India, although for some stays a lower validity period may still be accepted.