Hello

During the last preparation month, you should focus on revision. Revision is essential to score better in the exam. Also, you should practice online tests, it will help you in analysis of your preparation level and also enhance speed and accuracy.

You can also enroll for the BITSAT Knockout Crash Course for revision of the complete syllabus and practice mock tests-

http://bit.ly/2XZjurC

Good Luck!

Well to study in just one month for bitsat will be a bit difficult but not impossible. 

First thing is go through your text books, make your basic clear,  then you can go through the books which are made for this exams,  and go through their solved questions section to understand better and at last try to solve past year question banks.