I have completed my 11 th class now ,and am an aspirant of NIT Warangal,and how can I prepare for jee_main 2021????... and what are the important topics for thi exam ..can u tell me subject wise.it is my humble request to u sir.

Hello student each and every topic of class 11 and 12th are important as they are interrelated with each other don't skip any topic otherwise you may find difficulty later. Prefer NCERT to build your basic concept and make sure you do each and every example and exercise questions of Ncert before jumping to a reference book. After completing ncert thoroughly refer your coaching material or reference book as mentioned below -
Concept of physics by HC VERMA
OP TONDON CHEMISTRY
Rd Sharma Mathematics
Arihant practice book for Jee
You can also subscribe to careers360 knockout package for preparing and qualifying the entrance examination, refer to the link mentioned below - https://learn.careers360.com/knockout-jee-main-april/

Feel free to comment if you have any doubt
Good luck