Design

CAT is the most important part of the question paper. Start sketching and develop your own style of sketching and coloring. I cannot stress this enough. Good drawing skills are very important. How you present/draw your ideas is just as important as the idea itself. Keep reading the newspaper (especially around November-December) It will help you in GK part of GAT and help you generate better ideas. Most questions in CAT are related to current scenarios. . Based on the happenings and big stories in the media, plan and create small sketches. This way you'll save time on thinking during the actual exams. Go through various artists on social Medias, movies, art galleries etc. to find inspiration. Go through question papers from the previous years and see what kind of questions they ask. Start solving these question papers in the given time and work on pacing yourself
For that, you can pick up any reference book. Math, logic and English are mostly what you've learned in school but it's better to revise. Keep solving the previous question papers so you can get into the habit of thinking along those lines.
Check out other artist's work on Instagram, Pinterest, Behance, etc., so that you can improve your drawing skill and understand what the rest of the world is doing.
For GAT keep up with the news. Revise basic math/English and logic. Download question papers- time yourself when you solve them so you can understand where you stand.