Your choice of where and when to go will be determined primarily by the weather. India's vastness means that the climate varies greatly from region to region, and sometimes even from day to night, as in the desert regions. The Indian year features six seasons: spring, summer, the rainy season, early and late autumn, and winter, but effectively there are but three -- summer, winter, and monsoon.
You'll be better off visiting during the high-season winter months (Nov-Mar), when most of the country experiences pleasant, moderate temperatures (still hot enough to luxuriate in the pool), though cities in the north get chillier days as snow falls in the Himalayas. As a rule, always be prepared for warm to hot days, with the possibility of cooler weather at night. (If this has you worrying about how to pack, remember that you can pick up the most wonderful throwaway cotton garments for next to nothing and a real Pashmina scarf in every color to ward off an unexpected chill.) As with all season-driven destinations, there is a downside to traveling during peak months: From December to January, for example, Goa swells to bursting point with foreigners and city folk who arrive for the sensational beaches and parties. Lodging rates soar during these periods, so you may want to wait until the shoulder season (Sept-Oct, Mar-Apr), when there are fewer people and rates are very negotiable.
Summer (generally Apr-June) sees little traffic, and for good reason -- the daytime heat, particularly in India's north-central regions, is debilitating, even for the locals. This is the time to plan your trip to the Himalayas instead, particularly to high altitude provinces such as Himachal Pradesh and Ladakh in Jammu and Kashmir. Ladakh, a magical region in the far north of the country, can only be visited June through September -- the rest of the year it remains a destination that's strictly for hard-core adventurers looking to trek through ultraextreme cold conditions.
The monsoon drenches much of the country between June and September, usually starting its season in Kerala. Tamil Nadu and parts of Andhra Pradesh don't get too much rain during this period; instead they get more rainfall from a second monsoon that hits just this region around mid-October and runs through December. In Rajasthan, central India, and the northern plains, the rains typically arrive by July and fall until early September. Some of the regions are at their most beautiful during the monsoon, but it can be difficult to move around, and there is a higher risk of exposure to diseases like malaria. Flooding, power failures, and natural destruction are also not uncommon. We have noticed, however, that the monsoon has become increasing fallible and locals will tell you that global warming has had a devastating impact on the rains. These days, it's possible to spend most of June in Kerala and see only a few days of intense showers.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.