Hello,

IISER Aptitude test consists of questions from Physics, Chemistry ,Mathematics and Biology.The best method to prepare is by knowing the exam pattern.The exam is of 3 hour duration and there will be 15 questions from each subject.You can practice by solving previous papers and mock tests.This will help you in understanding the topics of high weight age and the type of questions asked.You can get the detailed syllabus and sample papers in the link below :

https://engineering.careers360.com/articles/iiser-syllabus-exam-pattern

Hope this Helps!!