Hi if this is your first trip to India, I would suggest doing just one region. As Eleanor mentioned, India will overload all your senses, especially on your first visit. Are you planning to do an independent trip, or go with a tour group? Either way, I would focus on either North India (the Delhi, Agra, Jaipur, Udaipur area) or South India (Kerala, Chennai, Mysore, etc. and stretch to Mumbai and Goa); they are both equally exciting but trying to do both in 3 to 4 weeks would be overdoing even if you aren't 'slow traveling'. North India will start to get cold by December. In South India, it never really gets cold (it is hot, hotter, and hottest). October November is good. for South India. December tend to be crowded in places to Goa because of Christmas