Hello

NCERT textbooks of Class 11 and 12 are very important for each section. You can clear the basics from NCERT textbooks. Most of the questions are asked from NCERT textbooks but some of the questions are asked form outside the NCERT textbooks also. So, reading and re-reading of NCERT textbooks is a must but you should also refer to other important books.
Check the details- https://medicine.careers360.com/articles/neet-2019

Good Luck!