In order to crack NTSE you should be dedicated and self motivated.

You should follow NCERT books for your preparation. You should Strengthen your MAT Section. You must read good general knowledge book. You should refer previous year papers to kow the exam pattern and level of questions. 

Solve complete mock test series to analyze your preparation level and to know your strength and weakness, So, you can work upon them. You should work on your speed as well.

R.S. Aggarwal’s handbook is extremely helpful for preparing for the MAT exams. For mocks, you can refer to Arihant & Tata McGraw-Hill books as they clearly point out the difficulty level of NTSE.

You should practice a lot to score good marks and make sure you revise your syllabus properly.

All the Best!!