The Actual Fact is in IIT Advance Paper the ratio of class 12: class 11 is approximately 60:40. In Class 12 study with full force and keep on clearing your doubts.
Clearing doubts is a very important aspect for an IIt Aspirant.
And Never leave any of your concepts uncleared
Be consistent with your studies i.e. never keep changing books follow only one and repeat it several times.
If you follow the above tips you can surely achieve your aim.
thank you