I would suggest you start your preparation to crack the exam with a good score here are some of the important tips you can follow for AIIMS preparation.

Know all about your exam

It is important to know as many details about the exam you are going to give as possible. For example, the syllabus, the exam date and paper pattern.

Work hard with consistency : You need to study 2 year syllabus in one year. If your basic concepts of class 11 are clear, studied from NCERT.

Follow subject tricks : See the trend of AIIMS past year papers. While solving questions, apply the tricks & Practice a lot and learn from your mistakes.

Make your notes : Making notes is very beneficial in your preparation. Make your own notes,The notes will be handy during revision. Include your own shortcuts and tricks.

Revision : Revision not in last few months, but every day. Go through all the things you learned during the day.

hii anand 

personally i would like suggest start from the day one of your +1 only because the demand for medical in our country is high and you have tough with the world i mean with our country where as you even give try for NEET as well 

hope this helps