Your ambition is very clear but the way to reach is serpentine.
You need to put approximately 4-5 hours per day in order to get an above average score in CAT. As CAT is not a cakewalk, high amount of dedication towards the goal is required.
You need to reduce all kinds of socializing possible and concentrate on CAT only.
Following these will surely throw you into a good college.
The key to a good rank in CAT is speed. You can start preparing 4-5 months before if you’re good at Math and Logic and if you have a good command over your English. Otherwise, starting a year before would be advisable, which would be right about now. Time your tests as performing well under the pressure is the way to a good rank.
Hope this helps.