Hello Pranav,

You have to score 180 to 220 marks in JEE Main to get a good NIT college. To achieve this goal, the most important thing is your confidence after that you should know the whole syllabus and make your plan properly for learning new chapters, solving the numericals and revision. All three things should be the part of your preparation strategy in daily routine.

Your basics in Physics, Chemistry & Mathematics should be very clear upto 12th std. You should read the NCERT books for basics. Then HC Verma for Physics, RD Sharma for Mathematics, OP Tendon for Physical & Inorganic Chemistry, and Organic Chemistry of "Arihant Publication" for detail or extra knowledge. 

You should also try to solve the previous years question papers, this helps too much and you should also give the mock test to rectify yourself and build your confidence level. In this way, you can make it possible.

All the best

You can Join NITs based on your score in JEE Main, your Home state, Your Category, and your Department. As Top NITS require good ranks while others don't. I would not recommend you to just join Any of the NITs. Even some NITs in North East remained vacant even after all the rounds of counseling. Some of the government colleges are even better than the NITs. I think you should Join NITs if you think you can get decent otherwise join any other govt college.

To get an idea of marks you can take help of Jossa opening-closing rank and using carrer360 rank predictor you can calculate the marks required for that.