Chemistry itself is an important subject and so are the chapters. You should prepare all the chapters very well. Never skip NCERTs. Though some of the important chapters I can mention :

Solid state

Solutions

Electrochemistry

Chemical kinetics

Surface chemistry

General Principles and Processes of Isolation of Elements

P block elements; D and F block elements

Coordination compounds

Total organic chemistry

Chemistry in every day life

It's not too hard to prepare for the boards. You have to go through all the chapters and solve exercises step by step. If possible try to solve previous years' exam papers by your own.