Hello Ria

Hardly months are left for the boards and so you need to put a lot of efforts if you want to score good.
Firstly, make a list of important chapters/topics having high weight age or from which maximum questions are asked every year. Then plan your schedule accordingly, so that you can cover maximum topics in a day along with it's revision and practice work.
Go for biology first and make a habit if studying it daily  atleast before your exam... So that you stay linked with the subject in which you can score maximum marks.
Try to make keyword type of notes.. which would help you till the end for quick revision of the entire chapter. Make separate note for the examples + the important diagrams. Practice each diagram 2-3 times .. because if you draw the complete labelled diagram in the exam and write less theory part.. then you'll surely get marks. So study in a smart way.

For Chemistry, go for the important chapters- take organic chemistry part first and clear your concepts/nomenclature and then go through the quick revision of the theory part. You need to write and practice the inorganic chemistry chapters for theory. Whereas, for Physical Chemistry part, concept matters the most. The mechanisms should be clear and on that basis you'll be able to write theory.

Lastly for Physics, only practicing it maximum can get you marks. Refer HC Verma reference book for clearing your basics and then start practice work from your textbook for boards first and then the last year question papers of boards.

So prepare well and study smart.!
Hope this helps.!!
All the Bestt.!

Here are some preparation tips you can follow to prepare your 12th boards:

Make your time schedule for study subject & topic wise & revision for the same after completing and Develop the daily targets. 

You can follow the NCERT books and do Practise with the previous year papers as much you can.

Note down the important points during your study.

After completing any topic you should revise it two or three times. So, that you understood that topic completely. 

 

Good Luck!