There is no any specific percentage requirement to get admission in AIIMS or other medical colleges…..simply if your preparation is good then you will get a good college. For better preparation you can follow some strategy as solving more mock tests, multiple times NCERT revision, regular Questions practice and analysis , doubt clear , pyq analysis etc. These all things you may help to achieve a best score and you will get admission in AIIMS or any best medical college.however,you must fulfill eligibility criteria of NEET exam.