For NTSE preparation you need to be thorough with all the subjects in the test.
For sst you need to be thorough with the entire NCERT syllabus because questions can be asked from any part of the book.
For science and maths you need to know a little more than the NCERT syllabus. You can follow any coaching centres material.
For mental ability you need to follow any standardized book that will cover all the topics required for the test.
For English you can read books and solve some practice papers .
Hope this helps and all the best.
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