Hello,
In December you can visit so many places in India but some of the best is :
1-Shimla, Himachal Pradesh
2-Thajiwas Glacier, Sonamarg, Jammu and Kashmir,
3-Manali, Himachal Pradesh
4-Dalhousie, Himachal Pradesh
5-Dawki, Shillong,
this is all my suggestion and choice is yours ! Happy to help you,
Keep Exploring :)