Rayof sunshine
I don't know whether you are on a package holiday or DIY. If you are on a package you will find that most hotels do a gala evening on Christmas Eve or Christmas Night and another gala evening on New Years Eve. Both of these gala dinners are usually included in the price of your package and although they are included check with your hotel as you may need to book a table.
If you don't mind where you eat there will be no need to book, even if you have to wait for a little you will get a table but if you want to eat at a particular restaurant it may be better to book, although last year it was not so busy.
The taxis do try to charge more over the Christmas/New Year period. In fact in our experience they did try to charge extortionate charges, we were told it would cost 500rupees for a journey that would normally cost 100 rupees we just walked away from them and said we would walk. They will then agree a price with you. But to avoid any misunderstanding it's always better to agree a price before you get in the taxi.