Most of India is tropical and impacted by monsoons. There are both dry and rainy seasons with rains more intense in some areas than others. Monsoon season is shorter in the northwest and non-existent inland where it is mountainous. Along the coast, India is hot all year, especially on the central and southern coasts. There is often a breeze that tempers the heat, however.
The wettest period is July to September, although in the southeast, monsoon season can lead to rain until December. Winter is December through February.
The best time to visit India is between late October and March when it is dry and cool.
The rail network in India covers almost the entire country with only a few mountainous regions inaccessible by train. The railway system may appear to be chaotic, but it works well. Trains are often late, sometimes hours behind schedule. When the train arrives, your reservation is pasted on the side of your carriage. There are overnight trains for long journeys. Be sure to padlock your bag to your bunk with the attached chain.
Plane travel is also popular between cities in India simply for the time it saves. A train trip from Delhi to Chennai takes 36 hours on a train but just over two hours by plane. Flights are more expensive than trains, but the cost may be worth the time savings.
Buses are another option, especially in the mountainous regions where trains cannot go. Government-run buses are often crowded with people, luggage and even livestock. Some towns offer private buses which are more comfortable.