How can I score more than 95% marks in class 12th science stream?

You can easily score 95% even if you start working now and prepare from the right book.
(Just assuming you passed in half yearly with atleast 60%)
I passed 12th last year only with 94.4% aggregate. And by this time(december), I just used to attend tuitions. No self study.
I started taking BOARDS seriously only after boards datesheet was out. (1st week of jan)
I’d just suggest you to mug up the NCERT books first and then practice from sample papers book on latest pattern.
Take pre-boards seriously.
As most of the time, your board practicals marks are awarded on the basis of pre-boards. Even externals also ask you about your pre-boards performance.
Not only this, pre boards will tell you your current status about how much you’re prepared for boards.
So,make sure you get 30/30 in three of the practicals.
Now, for theory exams I will explain for each subject what should be the correct strategy