Hello Dear,

there is no formula to score complete marks in Maths  class 12. There are certain rules which you need to follow:

Just focus on previous years questions/papers (starting from most recent)and ncert (both problems+solved examples)
(Also keep reading very old papers, in between whenever you have time, so as not to miss some very peculiar question that might've been asked back then). After completing your syllabus please revise it again and again and dont follow more books because it is better to revise one book 10 times rather than doing 10 books one one time.And do all soved examples and miscellaneous exercise of ncert.