The mistakes droppers should avoid in AIIMS are-

1) Negative Marking. Be very careful about not answering questions you are not sure about. Even one mark brings difference in of many ranks.

2) Be careful about the time limit. Practise more and more questions at home so you don't run out of time during exam

3) Be thorough with your concepts. Questions in AIIMS are more of conceptual basis than factual ones.

4) Be up to date with the GK and current affairs..

Good luck