As I can see, your question appears under the "management" section. So on a quick note, let me brief you in general. Any management exam would be primarily an aptitude test,  a test that checks your spontaneity,  time management and command over concepts. Let me tell you step wise. Three sections: Verbal Ability - that will comprise of reading comprehensions and questions pertaining to that-direct and inference based questions. Added to this there will be questions based on verbal ability like jumbled paragraph, spotting the incorrect or odd one out of the paragraphs. Good books are available for VA practice like "How to prepare for Verbal Ability and reading comprehension by Arun Sharma and Meenakshi Upadhyay".
Data Interpretation and Logical Reasoning(DI-LR) .- graphs will be dominant in DI and logical reasoning can range from blood relationship questions to seating arrangement questions to anything related to timing. Books that you can refer are: "How to prepare for logical reasoning by Arun Sharma",  "Logical Reasoning and Data Interpretation by Nishit K. Sinha".
Quantitative Aptitude.- basics of mathematics and it's concepts. Algebra, arithmetic, geometry and modern maths are the four broad concepts to be covered for nay exam. Book: "How to prepare for quantitative aptitude by Arun Sharma".
This was an overall view for preparation. For modes of preparation you can either join a good coaching centre, or go for a crash course if you lack time, join online coaching portals or you can read and refer books too. Online tests are recommended if you want to give online exams as they give you the best experience and idea of the exam. Or else such interactive portals like Careers360 are always there to help you and steer you through your way.
Wish you all the best! 
For clarification regarding any other exam, which I could not include in this text, do comment. Happy to help!!

Which exam preparation are you asking for?