If you say, in December - Do visit the heart of India i.e Madhya Pradesh specially Panchmarhi. The beautiful Pandav Caves and the Patalpani, Tincha falls..
simple yet beautiful not at all fancy places but not at all crowdy. can enjoy much
Rajasthan : Jodhpur, Jaisalmer and Jaipur
or Jaipur, Udaipur and Mount Abu Kasol and tosh- There will be multiple Musical festivals . one is planned for new year. Mcleodganj Manali : they have very beautiful home stays. Almorah