Hi there. 

Keep solving questions until your concept becomes crystal clear and you develop a problem-solving approach. Just for the sake of your question, it is advisable to do 250+ different types of questions from each chapter. Cracking the AIIMS examination comes at the cost of hard work, patience, determination, continued practice, and a lot of focus on proper time management.

The following books might prove helpful in your preparation. 

First of all, for all subjects i.e Physics, Chemistry, Biology study the NCERT books cover to cover at least twice. For Biology read NCERT as many times as possible. For only the text material of Biology, you actually don't need to refer to any other book. NCERT is more than enough for biology. You might doubt this but trust me NCERT is really really enough for Biology. I can't stress more on this FACT.

For Physics, after completing NCERT complete all examples and questions from DC Pandey Objective book of physics by Arihant publishers. Revise the material as much as possible.

For Chemistry, after completing NCERT, for physical chemistry do MCQ type questions from Vibrant Academy's book of Narendra Awasthi. It is a book for JEE but for AIIMS you only need to do and complete the TYPE 1 questions from that book and that will be enough. You will find direct questions in AIIMS from this book.

For inorganic chemistry, NCERT is enough. Read it as many times as possible. The same studying principle of Biology applies to Inorganic Chemistry as well.

For organic chemistry, solve Vibrant Academy's book by MS Chouhan. This book is specifically for NEET/AIIMS and will be enough to score high in the organic chemistry section.

For Biology, along with NCERT solve all questions from the book of MTG NCERT at your fingertips. Solve this book and revise it as many times as possible. 

LASTLY, your preparation would be incomplete if you don't solve previous years questions. For that refer to MTG chapter wise previous year question for all subjects i.e. Physics, Chemistry, and Biology.

Good luck!