There is no prescribed syllabus for AIIMS as it covers NCERTs so if you are preparing for NEET then it will help you in your AIIMS preparation as well but the only difference in AIIMS and NEET is there will be GK and Aptitude & Logical Thinking section so it would be better to read newspaper on daily basis just to get all day to day information and along with this, you can subscribe weekly or monthly current affairs magazine and pay proper attention to science section.

As the syllabus is more or less the same so no need to prepare separately but yes, the difficulty of AIIMS is higher than NEET so make sure you are preparing really hard and I am sure if you study seriously then you will crack these exams with flying colours.

Good Luck!!!