December to February are the best months to visit Jaipur. It is bit cold in the night and sunshine in the day time so it's a blend of beautiful weather to enjoy the city, it's architecture, food and shopping.
December and early January is the best time to visit Jaipur or any place located in the state of Rajasthan. During this time the temperature falls down to 12°c to 25°c which is ideal for travel as compared to 35°c to 50°c during rest of the year.
Pre monsoon or early monsoon are the best time to travel anywhere in Rajasthan especially Jaipur. In the season you can enjoy without any problem due to heat. Also, the mountains are lush green, the lakes are full and places like Jal Mahal, Hava Mahal are a treat to enjoy in the weather.