is NCERT enough to score good Mark's in JEE , by practicing NCERT ..

It is true that the JEE exam has is based on the syllabus of NCERT books , but it is not advised fully to rely on NCERT textbooks as the complexity of question asked in the exams are different from the books.

While preparing for JEE you must first read and learn the NCERT books completely & thoroughly to say about 3 to 4 times .

But you should also refer H.C .Verma , R.C Mukherjee and R.D Sharma

Also you should do many mock tests and study prievous years papers for getting a idea how tough is the JEE Exam.

Practice makes a man perfect.

All the best

Undoubtedly, NCERT textbooks are best for basic preparation and having a clear concept of all the subjects for Jee Main and board as well. But to fetch good percentile in Jee Main, you must go for solving complex problems. So you should follow some standard reference books like Concepts of physics by HC Verma, Problems in General Physics byI.E Irodov,  Mathematics RD Sharma and Plane Trigonometry by S L Loney, Physical Chemistry by OP Tondon, Numerical Chemistry by P.Bahadur, Organic chemistry by OP Tondon.