You have to be very good at numbers and geometry. The best way to prepare for this section is to pick up a guide on Quantitative Ability and start working on the basics.
Make it a goal that in the next three months, you have to complete the basics of all topics CAT covers.
The typical CAT Quantitative Ability questions are based on simple equations, ratio proportion and variation, percentage, profit and loss, numbers, indices, logs and surds, averages, mixtures and alligations, quadratic equations, progressions, time and work.
Time and distance, geometry and mensuration, permutations and combinations, probability, special equations, inequalities, number systems, functions and graphs, coordinate geometry and miscellaneous math logic.
Mock tests are also perfect criterion to clear doubts and know the level where you are so that further improvement can be done.