Hello Kaushlendra Singh Rathore, Joint Seat Allocation Authority (JOSAA) Conducts 7 rounds of Counselling for IIT's, NIT's, IIIT's and GFTI's. you have to give your preference before the starting of Counselling,i.e at the time of choice filling. Usually in the starting rounds people don't get a good seat but after some rounds you can get a better seat as some people who gets seat both in NIT's and IIT's have lefts a seat and candidates are upgraded to a higher preference, so you should wait till the 6 or 7th round to accept a seat as you will get a better seat there.

And there is 2 special rounds of Counselling held for NIT's if the seat remains vacant in some branches in different NIT's so, you should participate in special rounds as you will get a much better seat in special rounds as many peoples don't participate in special rounds.