NCERT is useful because it consists of all the concepts required. 

It is also useful as it contains exercises after each chapter. You need to solve every question on your own. Of course if any doubt occurs then you can refer to answers given. 

NCERT is very useful but I would suggest you to solve problems from different books also. For example HC Verma for Physics. In this book there are innumerable numericals for a student to solve. 

Keep reading or solving questions from different books so that you can score 250+.

Remember to give every subject an equal attention. 

If you still have any queries feel free to ask in the comment section down below. 

All the best