Sir your question is not clear,if you want to know eligibility to join NIT,then you must see eligibility to jee mains,if you score good in jee mains you will get NIT- eligibility link of jee mains shared below--

https://engineering.careers360.com/articles/jee-main-eligibility-criteria

If you want to know class 12th preparation tips then get onto this link--

https://school.careers360.com/articles/cbse-class-12-preparation-tips

For admission to IITs, NITs, IIITs, CFTIs, a general and OBC candidate needs to have at least 75% marks in the qualifying examination or be in top 20 percentile of the respective board. Now if you have less than 75% in 12, but if you are in the top 20 percentile of your board, then you will be eligible. If you match the criteria of Jee Main, you can appear for the examination. http://engineering.careers360.com/articles/jee-main-eligibility-criteria JoSSA conducts the counselling process for admission to NITs, IIITs, CFTIs etc. If you meet the cutoffs of various NITs you have to appear for JoSSA counselling and you'll be allotted to that NIT of which you meet the cutoff. Generally, for a general candidate, NIT seats are filled within 40,000 rank. So scoring 98.5 percentile can fetch you seat in any of the NITs.