Hey Aspirant, 

First thing is knowing the syllabus, exam pattern, marking scheme and other details about the ICAR AIEEA exam. Then accordingly you should plan making a routine which covers your all sections and topics. You can also give some extra time to your weakest subject.

Your best book is NCERT which covers the entire portion of PCB (Class 11/12). Questions from GK are also expected so prepare accordingly.

Revise what you studied timely so that the concepts are understood or else you can forget whatever you studied.

You can make short notes on a daily basis which you have studied. Write all formulas in separate notebook. You must follow your syllabus books along with some reference books.

Before completing your preparation, give online mocks and tests to analyse your preparation. You will get a lot of help through tests as it will help to improve your weak areas.