Only practice can make you perfect in any anything . Practice previous year questions, search for books which can be helpful. Clear your doubts and the most important thing try to understand the questions as soon as possible, this will provide you an extra edge
Try solving as many questions as you can.For basics you can start with class 9 and 10 books .then go for arun sharma .After doing this give online exams ,this way you will have the confidence to solve any question in the exams.