First of all, know the syllabus properly and get a perfect idea of what you know or remember in a better way put then in section A. Recollect the topics that you know but are not sure and need to revise put them in section B. And the tough topics which you have forgotten or don't know put them in section C. And accordingly spend your time for each section in a smart way. For calculus, series, etc topics use the GK Gate Preparatory Maths book. For linear algebra, watch some videos from YouTube to clear your basics and then go for solving more. You can take help of videos from MIT professor Gilbert Strang. Do not waste time by learning maths from some standard books, you will end up without completing your syllabus. Just go quickly through the topics of your section A and section B by using YouTube or GK Gate book. And give a but of time for section C topics that's it.

Thankyoi. Best wishes.