Hello Devendra Yadav. Thanks for contacting Careers360 and we hope we will be able to answer your query. 

Note that the IISERs are among the few academic institutions in the country that accept JEE Advanced scores for admissions other than the IITs. So, obviously the level of input you would have to put into your preparation is very high. 

The eligibility criteria on the basis of Advanced ranks is as follows:

• Candidates in General category securing a rank within 10000 in the Common Rank List (CRL) of JEE Advanced 2018 are eligible to apply.
• For candidates belonging to reserved category (OBCNC, SC, ST, PD), their category rank should be within 10000.

I would like to direct your attention to this Careers360 article for upto date information on the cutoffs for the IISERs:

• https://engineering.careers360.com/articles/iiser-merit-list-and-cutoff

Also, please see here:

• https://www.entrancecorner.com/engineering/iiser-2017-cutoff/

Hope this helps you and all the best!