I am answering for general category. For getting into top 10 NITs with a decent branch you must get rank below 10000 which you can get by getting morethan 98.5% in JEE MAINS.

Hello there,
You haven't mentioned some details like your category, the branch you want to choose, and your home state. Nevertheless, I'm answering your query assuming that you are from the general category. For getting a seat in the top 10 NITs, you have to rank below 7000. Your percentile should be atleast 98.5, or 99 to be on the safe side. For this percentile, you need to score 220+ marks in JEE Mains 2020. It seems difficult but it's not impossible. If you try hard, you can achieve it.
Hope this answer helps you.
Good luck!!