sir how to study for class 12 Math in bihar board for good marks in one month 

Basically I am studying in class 12th science stream From maths background
And want to crack mains too next year so guide me??

Well, in that case, NCERT might not be enough. Apart from it, you can refer to various other books like that of HC Verma for physics, RC Mukherjee for chemistry etc. These books contain very basics to advanced level questions. Also, if you are interested then you could also join a coaching center where they will guide you and provide you proper materials.

For boards NCERT is enough ???

Yes!