It depends on your place of interest. If it is mountains or hill stations - Visit Kufri a station above Shimla. Best way to travel: Delhi to Kalka by Train and then Kalka to Shimla by a toy train. ( Himalyan Queen)
Book tickets in 2 months advance. If you want to visit plains, they are best in winters. - Go to Khajuraho- Madhya Pradesh. Ajanta or Ellora Caves in Maharashtra, For beach destination plan: Andaman I would not recommend GOA for your honeymoon trip.
If December hill stations will be super chilled and Kashmir will be a little tough choice. Though snowfall there will be awesome if you can bear the cold. Else you can visit Kerala especially it's back waters or You can got Rajasthan.
Hey you can have a look at the following destinations which are super awesome for a honeymoon: 1. Kohima, Nagaland: It is a True Gem in the Hills 2. Manali, Himachal Pradesh: Located in the gorgeous Green Beas Valley 3.Lakshadweep: Turquoise Lagoons & Secluded Beaches 4. Jaisalmer, Rajasthan: A Shimmering Land