how I prepare to CAT exam

Joining Coaching Institute is recommended namely TIME/Careerlauncher/IMS/CATking. If you're done with preparation or Once you're completed with studying you should appear for atleast 20mock exams including previous year's papers. Try to analyze your mock results, by judging how much time you devote to wrong questions, how many questions are unattempted, how much more you could have done, what questions consume lot of time. Accordingly you can identify weaknesses and focus and revise on them to convert it into strengths. For last one month, its advisable to revise mistakes and weak areas if any, and relax alot to stay calm for Final day. You should finalize your test taking strategy by this time. For mock exams go with websites like TestFunda, Oliveboard, HitbullsEye. Recommended books are Arun sharma for Quants, Nishit Sinha for Data Interpretation, and Arun sharma for Verbal ability and Logical Reasoning. 'Word power made Easy' is also good for Verbal section.

CAT will be conducted by IIM on 26th November this year and less than three months you have to practice and crack it. CAT  is more about smart work than hard work.Firstly if you can join any coaching institute, go for it. Coaching institutes can guide you how, what and when to study. When preparing  you will come to know about your weaknesses and strengths. As time is constraint you need to practise at least 3-4 hours a day. If you can't join a coaching institute then Get material from the coaching institutes like TIME, Career Launcher, PT education etc and refer following books for preparation.
For Quant you can refer Arun Sharma and Sarvesh Verma. Just buy one of the above. That will be more than enough if you complete the whole book.
For data interpretation  and logical reasoning you can refer coaching institute material from Handa ka Funda IMS / TIME / Career Launcher as your first resource. This material is very well designed and keeps the needs of students as the first priority. If you still need books then you can go for Arun Sharma's 1. How to prepare for Data Interpretation for the CAT
2. How to prepare for Logical Reasoning for the CAT or you can also refer books by pearson, Nishit K. Sinha for all topics.
For verbal you can refer 'word power and easy' by Norman Lewis and 'How to prepare for verbal ability and reading comprehension' by Arun Sharma & Meenakshi Upadhaya.

You can go through this link for topics you need to prepare for CAT.

Read newspaper everyday for verbal ability as it will help in reading comprehension, vocabulary and your reading speed will be enhanced. Also read few more books during the preparation for vocabulary and general awareness (fiction, biographies etc) and stay positive and work on your strengths and weaknesses.

And keep taking mock tests and analyse result after every test you take.

You can also try various videos on YouTube about how to crack the exam.

All the best!