CAT

Here are two things to keep in mind:
The problem reading time must be reduced. You should be able to read a question and translate it into variables and/or diagram/equation at one shot. Most students read a question slow/multiple times with an intrinsic fear of getting it wrong otherwise. Practice reading fast. We seldom realize that toppers save half the time in reading and understanding the questions faster than others. The problem solving time can be reduced. Conceptual/process memory builds if you have solved different types of questions multiple number of times. I suggest a student should revise his/her coaching books/sheets at least 3 times before CAT. Look at CAT teachers, they solve questions so many times that the types become very clear to them and the solving process comes naturally to them. The difference lies in the process memory. I have solved questions so many times that I can think faster and solve faster than before. A student can become up to 100% faster than before by practicing limited content (which includes problem variety) multiple number of times. Most students find this re solving boring and ignore it. You must not do that. Revise!
Learn fast track tools: basic mental multiplication techniques, squares, fractions and approximation techniques (based on trend analysis in the numerator/denominator). Learn how to structure constraints in LR; learn methods for syllogism; practice 34 variable sets and matrix formation. Knowing these techniques saves time. Give lots of timed tests: Speed tests/sectional tests/topic tests - I would say: at least 50 such tests per section must be taken. Helps you manage hormones in the exam hall - teaches you to focus hard in a short span of time (normally such tests are 20 minutes to 60 minutes in duration). With practice, you become skilled to sit for 3 hours with full focus and speed.

First of all, both CAT and GMAT have different patterns. Although, both measure a person's abilities like Quantitative and verbal, but the content differs. GMAT is an adaptive test, which means as you answer the question right, a harder question will be given to you and if you answer wrong, a question easier or equal to your last question will be given. You can move forward only if you answer the current question. Whereas, CAT is a linear test where questions are numbered and you can go back and forth anytime and choose which question you want to answer first. The verbal ability parts of both the exams are somewhat different. While GMAT has Sentence Correction, Reading Comprehensions and Critical Reasoning. CAT has some similar question types but it focuses more on grammar and vocabulary. GMAT also has Analytical Writing Assessment and Integrated Reasoning which is different from Logical Reasoning and Data Interpretation questions in CAT. So Preparing for CAT may somewhat help, but since the pattern differs you have to study according to the question type and timing of the exam. Again, GMAT requires SMART studying whereas CAT requires a lot of practice.