CAT

Hi Sidak,
Yes, the two exams you have mentioned are poles apart. CAT/UPSC is a very common doubt among people when they start considering future options.
1. Become a voracious reader of newspapers (The Hindu/ Indian express). This would help you with the following:
A. Your reading ability goes a few notches above, your vocabulary is bound to be enriched and these are areas which at any given day is going to help you with the Verbal part of management exams which is tested.
B. Your knowledge content goes leaps and bounds ahead and suddenly you would, which will inevitably provide you with a strong foundation of 2 out of 4 GS papers (General studies). Every civil aspirant goes through this newspaper for hours on a daily basis.
2. Aptitude: This is a part which is tested by both the exams (The difficulty is definitely a bit higher for CAT than UPSC), but the fundamentals or the syllabus is 10th Grade mathematics. My suggestions for the same:
A. Quantitative ability: Please refer to standard books by Arun Sharma, the approach of the book is quite generic and complete it in entirety and keep developing your quantitative problem solving skills. There are a lot of books other than Arun Sharma for the same.
B. Data interpretation and Logical reasoning: Right from solving crossword puzzles to Shakunatala Devi, keep tuning your mind to exceptional level of analytical and reason/logic based thinking.
With the above two you would obviously be clear to CSAT Prelims and CAT at the end of two years, and with a time frame of 700-800 days you would be in a situation to prioritize on a stronger note and follow your gut based on hard-work and inputs.
Hope this information helps. Please feel free to revert.
Wish You Luck!