It is important to take basic precaution during India tour in winters. Severe winter ranges from mid December to mid January. In some hilly areas it may stretch for longer period. The severity may occur anytime hence one has to be prepared to face it.
Exposure to cold could be more frequent and extensive hence on needs to be best equipped. Warm inner, sweaters, jackets, socks, head gear and hand gloves should be with the traveler all the time. Some basic accommodations may not have a heating system hence an extra quilt should be in one's bag always.
High altitude may not suit travelers with breathing problems hence should be avoided. Places above 1400 m can be quiet uncomfortable for such travelers.
It is wiser to carry all prescribed medicine for those susceptible to cold and high altitude. The cold is not restricted to North India it can be severely cold in Rajasthan and Madhya Pradesh at Places. A good doctor may be able to give apt advise to travelers in India during winters. Masala tea or ginger tea proves very good for cold and cough. Try it! Any chaiwala will make you a ginger tea.
Due to fog flights, rail and even road traffic may come to a stop hence on should keep an alternate travel recourse well planned in advance. Even tough winter is a healthier season in India road side food and water should be avoided at all cost.
It is better to make your trips during the day and return to hotel in the evening since the cold gets worse after sunset. The nature is at its best during the winters and the landscapes splendid enjoy your travel in this incredible country.