Pattern of the exam
The exam consists of 200 questions out of which 40 are multiple choice questions in the subjects of Physics, Chemistry, Biology each, 20 in G.K. and the rest 60 are Assertion-Reason type questions equally divided between the subjects of Physics, Chemistry and Biology.

AIIMS V/s other PMT’s
The paper of AIIMS is quite different from other PMT exams and demands a little care during the preparation for an assured selection. The questions asked are not that straight-forward as they might appear at first sight. It requires concentration, presence of mind and above all confidence that whatever you are marking is true and that you are doing full justice to the question. It is popularly but wrongly believed that graduation level studies are required for aiIms preparation. It is not. Concentrate on the basics. 

Requirements of a good AIIMS preparation plan
1. Don’t over-expect. Don’t take an extra pressure on your head for AIIMS preparation. The other tensions are already enough. 
2. Just keep cool and prepare but keep in mind that for any other PMT and so also AIIMS you should go through the text thoroughly.
3. Don’t simply cram facts. Understanding is more important and definitely pays when required.
4. Don’t hesitate to clear your doubts. Don’t have that feeling that you don’t know anything. Everyone has his doubts. After all a rose also has thorns. You are the rose and have to remove your thorns one by one.
5. Start from the important topics so that they are not left out.
6. Try to do the maximum. But remember that you cannot remember everything. Its human to forget. Caution: Don’t try to make this tip an excuse. You must remember the maximum as I said, if not everything. After all the competition demands you to be perfect.
6. Share problems with parents. Be it be related to your emotions or to your preparation. This will let you come back on track and concentrate on your studies again.
7. Concentrate on your G.K. You need to keep a track of the events of the past year, besides the basic facts.(HINT: Nobel prizes and other awards are very important)
8. Have a clear concept. This will help you maximum during assertion reason type questions solving.
9. Read quality magazines like Exams Today and not just any others of the plethora available on the book stalls. These magazines present a wider application of the various concepts related to your studies. Such concepts are often asked in the AIIMS paper as assertion reason type or in the conventional MCQ type questions. I found ETG(EduSys) test series and correspondence course material useful for the AIIMS PMT preparation.
10. Read HYFs available in the above mentioned magazines and correspondence course to revise a day before the examination as there is no time to go through the entire books again.

Strategies at the test centre and during the exam
1. Have a light breakfast to avoid tiredness and sleepiness during the exam.
2. Reach the test centre well in time to avoid any anxiety.
3. Don’t talk to people. They will always try to push you deep in the sea of pressure in which you are already floating. Try talking to your parents to keep yourself relaxed.
4. Don’t unnecessary feel that “I can’t believe today is the AIIMS paper”; or “What will I do now, I am not prepared” and other self-demoralizing thoughts like these. Be relaxed, it is just another exam and not an appeal against a death sentence.
5. Read the question carefully. A miss of a word and it could cost you a seat
6. Plan the course of attempting the paper. Gauge its length. Otherwise 3.5 hours are enough I think.
7. Don’t go for absolutely wild guesses. Negative marking is stiff.
8. Be careful about the correct marking of answers. Also ensure that the non-writing hand which we generally keep on the answer sheet does not have a pen mark or a stain which may spoil it.
9. After the exam, feel relaxed. You have done what you could. Don’t think much about the exam. Your job is over now. Now it is the examiner’s turn.

The Biggest Myth
The biggest myth about the exam is that Assertion Reason type questions are a hurdle which cannot be crossed.
For such questions read the text book thoroughly. Read the text book as if trying to find out a reason for every line written. With practice you will develop this habit and subconsciously grasp the chapter as if it written in the form of an Assertion and its Reason. Presence of mind is also required for proper judgement of the correct option especially the choice between a (if both A and R are true and R is the correct explanation of A) and b (if both A and R are true but R is not the correct explanation of A). 
Practise such questions from the ETG magazines and ETG’s publication, Assertion Reason Type questions for AIIMS.
Follow my suggestions, of course with your own modifications, for success in the exam.
ALL THE BEST!!!