Ideally CAT preparation is not something which can be done in a short time. The best way to prepare would be to take a really long time of over 1.5year. For example, if someone wants to appear in December 2019, the preparation should start from March 2018. Break up the preparation as follows
1) March to September: Get basics correct. DO NOT aim to have a quick speed. Rather focus on a better accuracy of answers. Even if solving Quants and DI and LR take a long time, ensure that your answers are correct. Also, focus on improving grammatical skills as that turns out to be very important in the verbal section. The aim should be that by the end of September, whatever question you solve, it should be correct. Even if it means that you take 4-5minutes to solve one single question.
2) September to December: Take mock tests and solve papers. Try to get into the groove of appearing for CAT. This will help somewhat to improve speed. Note, accuracy will definitely go down if you try to drastically improve speed. So be slow and steady. In December, appear for CAT, NMAT and any other management exam you target. This will be just a trial. See how you fare in those.
3) January to July: Work on speed and improve the speed keeping accuracy intact. By this time, you should have a hang of how to solve questions. The questions which used to take 3-4 minutes to solve, should now take 2 minutes. You should be able to save 2 minutes as you dont have to explore how to solve the questions. Over time work on improving speed and ensure that accuracy level goes up.
4) July to November: Concentrate only on Mock Tests. Take up AIMCAT(This is a personal recommendation) or any other test series for CAT. Your preparation should be over by now. The full focus should be on appearing for Mock tests and ensuring that you are well accustomed to the exam scenario.
Following this, I think it should be a cakewalk in the CAT exam.
People might think this is too long a time, but that is the way it should be. Shortcuts only will never help you crack the coveted institutes and in the current market scenario, nothing but the best will help you progress.