Is dropping an year for AIIMS is fine or should I try in this year only ?

You should not drop a year you can start your preparation and try to get admission in 2018. You have plenty of time. You can manage between your boards and entrance exam as syllabus is same for both but level of AIIMS exam is high.

Below are the important topics for AIIMS you should focus more

Biology:  Systematics, Genetics, Cells, Ecology and Human Health & Diseases are especially important.

Chemistry: General Organic Chemistry (EXTREMELY IMPORTANT), Hydrocarbons, Equilibria, Bonding etc. Also, be very thorough with reactions of p-block elements.

Physics: Modern Physics, Waves, Heat and Thermodynamics, Ray Optics etc.

Below is the recommended books for your preparation

Physics:

CBSE PMT by P. Aggarwal (set of 3 Volumes)
HC Verma (Volume 2)
Biology:

Pradeeps
Truemans Biology (Volume 1 and 2)
AC Dutta for Botany (Oxford Publication)
MTG (Biology Today) CBSE PMT (magazine)
Chemistry:

ABC Chemistry
Organic Chemistry: Arihant Publications, Morrison Boyd
Physical Chemistry: Peter Atkins and Julio de Paul
A New Pattern Textbook of Inorganic Chemistry for Competitions by O P Tandon
Objective NCERT at your fingertips Chemistry by MTG

All the Best!!