You can consider below tips -

1. Know your Syllabus Well.
2. Work on a Time Table.
3. Make your Basic Concepts Strong.
4. Improve your Weak Points.
5. Write Notes and Prepare Flash Cards.
6. Attempt Mock Test and Solve Sample Papers.
7. Revision plays a vital role.
8. Make Sure to Take Breaks.
9. Check out Proper Books for Preparation.

Books which you can refer -Biology -

NCERT Biology of Class XI and XII Trueman's Biology Vol 1 and 2 Objective Biology by Dinesh Pradeep Publication's Biology GRB Bathla's Publication's for Biology

Physics -

Concepts of Physics by H. C. Verma NCERT- Physics Part 1 and Part 2 D C Pandey Objective Physics Fundamentals of Physics by Halliday, Resnick and Walker Problems in General Physics by I. E. Irodov

Chemistry -

NCERT Chemistry Physical Chemistry by O.P. Tandon Organic Chemistry by Morrison and Boyd for Organic Chemistry Modern’s ABC of Chemistry for class 11th and 12th Concise Inorganic Chemistry by J. D. Lee for Inorganic Chemistry Dinesh Chemistry.

Hope this helps!!!

In order to start your preparation you should be aware of the exam pattern and syllabus of the exam.

To score good marks in AIIMS make sure your basics are clear. You can take  help of NCERT books to build your concepts and make your fundamentals strong.

Below is the subject wise preparation

Physics - This subject tests your analytical skills. The physics questions in the AIIMS exam are advanced, but if your concepts are clear, then you can easily solved it. Practice as many Assertion & Reasons questions as you can.

Chemistry – In the past, most of the questions have been NCERT-based. Hence, refer to NCERT books for practice.

Biology – Follow NCERT & the Trueman’s series of books.

General Knowledge – You should read newspaper and magzines for your knowledge.

You should refer previous year papers to understand the exam pattern and level of questions. Solve as many as mock test series to know your strength and weakness. So, you can work upon them. You should also work on your time management.

At Last, It is not easy to crack AIIMS you should be motivated and determined to crack your exam. Don't loose hope and Stay Positive.

All the Best for your Preparation!!