Hi,
Be thorough with NCERT (Physics, Chemistry and especially, Biology) books of 11and 12 standard, Solve previous year questions papers, Focus on important areas.
Physics- Mechanics, Optics, Thermodynamics and Nuclear physics.

Chemistry- Mole concept, General organic chemistry, Periodic table, Chemical bonding, Coordination chemistry.

Biology- Ecology and environment, Genetics, Cell Biology, Morphology of plants and animals, Reproduction in plants and animals, Physiology of plants and animals, Basics of Biotechnology

Try to solve as many mcqs for your practice and  also solve complete mock test series.

You can even find some good tips for AIIMS preparation from this link below:
AIIMS Preparation

Good Luck.

All India Institute of Medical Sciences MBBS Entrance E ...

Result | Eligibility | Application | Exam Pattern | Admit Card | Preparation Tips | Cutoff

Get Updates Brochure