To score good marks in ICWAI exam you should Study Notes of the Institute for all subjects supplemented by other books recommended by your faculty. Following are some tips which will help you in getting good marks:

Make brief notes of the matter
Make a plan of the time available and the syllabus to be covered.
Ensure two revisions before you appear for the examination.
Study the question papers of previous examinations
Refer to a number of text books for these subjects
Practice use of your calculator effectively to maximize its efficiency in the examination Hall.